A nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst and applications thereof

Abstract

The application relates to a nitrogen, sulfur and boron co-doped carbon-based metal-free catalyst and application thereof, wherein the nitrogen, sulfur and boron co-doped carbon-based metal-free catalyst is prepared by the following method: dissolving a zinc salt and a sulfur-containing precursor in methanol, the molar ratio of zinc ions to sulfur being 1:1-1:10, to obtain solution 1; dissolving 2-methylimidazole in methanol to obtain solution 2; adding solution 2 into solution 1, the molar ratio of zinc ions to 2-methylimidazole being 1:4-1:10, and then ultrasonic treatment and standing; centrifuging, drying and calcining the precipitate in an inert atmosphere to obtain black powder; placing the black powder and a boron source in a porcelain boat at the lower and upper air inlets of a tube furnace respectively, the mass ratio of the black powder to the boron source being 1:1-1:20, and calcining in an inert atmosphere to obtain a catalyst NCSB-1 with a dodecahedron structure. The catalyst has high activity, the preparation method is simple, and the production cost is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, specifically to a nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst and its applications. Background Technology

[0002] The long-term use of fossil fuels has led to severe environmental and climate problems. In energy conversion and storage devices, metal-air batteries use active metals (such as lithium, zinc, and aluminum) as the negative electrode and utilize oxygen from the air as the positive electrode active material. With its open air electrode structure, it can theoretically achieve energy densities far exceeding those of traditional batteries, thus being considered an important development direction for next-generation high-energy storage systems. The oxygen reduction reaction (ORR) in the cathode of a metal-air battery is a key factor limiting its energy conversion efficiency. Due to its slow reaction kinetics, it relies on highly efficient catalysts to lower the reaction energy barrier and improve electron transfer efficiency. Currently, widely used platinum-based catalysts, while exhibiting excellent activity, face problems such as high cost, resource scarcity, and insufficient stability (e.g., dissolution, agglomeration, and poisoning). Therefore, research is shifting towards developing alternative materials that combine high catalytic activity, excellent stability, and low cost, aiming to achieve breakthroughs in ORR performance by controlling electronic structure and active sites.

[0003] Compared to noble metal-based catalysts, metal-free carbon-based catalysts exhibit several significant advantages in the oxygen reduction reaction (ORR), making them a research hotspot in fields such as metal-air batteries. These catalysts, primarily composed of carbon materials, not only have widely available raw materials and low preparation costs, but also possess tunable electronic properties, excellent structural stability, and outstanding resistance to poisoning, demonstrating enormous application potential. Specifically, the core advantages of metal-free carbon-based catalysts are reflected in the following aspects: First, they completely avoid the use of expensive and scarce noble metals such as platinum, greatly reducing manufacturing costs; second, by doping the carbon framework with heteroatoms (e.g., introducing elements such as nitrogen, sulfur, boron, and phosphorus), the local charge distribution can be effectively adjusted, breaking the electroneutrality of carbon materials and forming sites with high catalytic activity; third, through defect engineering (e.g., constructing vacancies and edge sites) and pore structure design, the specific surface area can be increased, mass transfer pathways optimized, and more catalytic active centers exposed, thereby significantly improving the catalytic efficiency and 4-electron selectivity of ORR. Furthermore, these catalysts maintain high stability in complex electrochemical environments, are not prone to common phenomena such as agglomeration, dissolution, or sintering, and are particularly suitable for long-term operating conditions. Therefore, developing metal-free catalysts is of great significance for improving the performance of oxygen reduction reactions. Summary of the Invention

[0004] One object of the present invention is to provide a nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst, which solves the problem of high cost of precious metal catalysts in the prior art; another object of the present invention is to provide the application of such a nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows: This nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst is prepared by the following method: Step 1: Dissolve the zinc salt and sulfur-containing precursor in methanol, with a molar ratio of zinc ions to sulfur of 1:1 to 1:10, to obtain solution 1. Dissolve 2-methylimidazole in methanol to obtain solution 2. Step 2: Add solution 2 to solution 1, with a molar ratio of zinc ions to 2-methylimidazole of 1:4 to 1:10, sonicate, and then let stand. Step 3: After centrifuging and drying the precipitate obtained in Step 2, calcine it in an inert atmosphere to obtain a black powder; Step 4: Place the black powder obtained in Step 3 and the boron source in a ceramic boat at the lower and upper air inlets of a tube furnace, respectively. The mass ratio of the black powder to the boron source is 1:1 to 1:20. Calcinate in an inert atmosphere to obtain the dodecahedral catalyst NCSB-1.

[0006] In step one of the above scheme, the zinc salt is zinc nitrate hexahydrate; the sulfur-containing precursor is one of thiourea, sodium thiosulfate, ammonium sulfate, sublimed sulfur, thioacetamide, dimethylamine sulfide, and potassium thiocyanate.

[0007] In step two of the above scheme, the ultrasound time is 0.2 to 8 hours, and the settling time is 24 to 96 hours.

[0008] In step three of the above scheme, the calcination temperature is 800~1500℃, the calcination time is 1~8 hours, the heating rate during calcination is 1~30℃ / min, and the inert gas used is 99.999% Ar or N2.

[0009] In step four of the above scheme, the boron source is one of the following: boric acid, borane amino complex, sodium borohydride, sodium tetraborate, metaboric acid, sodium metaborate, and boron oxide.

[0010] In step four of the above scheme, the calcination temperature is 400~1500℃, the calcination time is 0.5~10 hours, the heating rate during calcination is 1~30 ℃ / min, and the inert gas used is 99.999% Ar or N2.

[0011] The aforementioned nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst is used as an air cathode in the oxygen reduction reaction of a zinc-air battery. Beneficial effects

[0012] (1) In this invention, thiourea and boric acid are selected as sulfur source and boron source, respectively. Nitrogen, sulfur and boron co-doped carbon-based metal-free catalyst is prepared by high-temperature calcination. Sulfur and boron elements are successfully loaded on nitrogen-carbon materials. The two are evenly distributed and have a synergistic effect, resulting in a highly active metal-free carbon-based ORR catalyst.

[0013] (2) The present invention exhibits excellent activity and stability in catalyzing the oxygen reduction reaction under alkaline conditions, which is superior to commercial Pt / C. When applied to zinc-air batteries, it has high power density and long-term cycle stability.

[0014] (3) The catalyst preparation method of the present invention is simple, the raw materials are cheap and readily available, which greatly reduces the production cost. Attached Figure Description

[0015] Figure 1 This is a SEM image of the nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst obtained in Example 1; Figure 2 These are the XRD patterns of the carbon-based metal-free catalysts of Example 1 and each comparative example. Figure 3 The nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst obtained in Example 1 and the comparative example were compared at 0.1 mol L⁻¹. -1 ORR linear sweep voltammetric curve in KOH solution; Figure 4 The figures show the discharge polarization curves and power density curves of the nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst obtained in Example 1 and the comparative example used as the air cathode of a zinc-air battery. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings: Example 1:

[0017] The preparation method of this nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst is as follows: 1. Dissolve 2.38 g of zinc nitrate hexahydrate and 0.61 g of thiourea in 50 mL of methanol to obtain solution 1; dissolve 2.63 g of 2-methylimidazole in 50 mL of methanol to obtain solution 2. 2. Add solution 2 to solution 1, sonicate for 30 minutes, and let stand for 24 hours; 3. After centrifuging and drying the above-obtained precipitate, place it in a tube furnace and calcine it under a nitrogen atmosphere. Treat it at 950°C for 3 hours with a heating rate of 5°C / min to obtain a black powder. IV. The black powder obtained above and boric acid were placed in a ceramic boat at a mass ratio of 1:1 at the lower and upper air inlets of a tube furnace, respectively. The mixture was calcined under a nitrogen atmosphere and treated at 900 °C for 2 hours at a heating rate of 5 °C / min to obtain NCSB-1.

[0018] The nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst prepared in Example 1 was subjected to structural characterization and performance testing.

[0019] like Figure 1 The image shown is a SEM image of the nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst obtained in Example 1, indicating that the catalyst obtained in Example 1 has a dodecahedral structure with a size of approximately 350 nm.

[0020] like Figure 2 In the XRD pattern of the nitrogen, sulfur, and boron co-doped carbon-based metalless catalyst obtained in Example 1, 24° and 43° correspond to the (002) and (101) crystal planes of graphite carbon, respectively. Example 2:

[0021] The only difference between this embodiment and Embodiment 1 is that the sulfur-containing precursor in step one is sublimated sulfur. Example 3:

[0022] The only difference between this embodiment and Embodiment 1 is that the ultrasound time in step two is 1 hour. Example 4:

[0023] The only difference between this embodiment and Embodiment 1 is that the resting time in step two is 48 hours. Example 5:

[0024] The only difference between this embodiment and Embodiment 1 is that the calcination temperature in step three is 900 ℃. Example 6:

[0025] The only difference between this embodiment and Embodiment 1 is that the calcination time in step three is 2 hours. Example 7:

[0026] The only difference between this embodiment and Embodiment 1 is that the heating rate in step three is 3 °C / min. Example 8:

[0027] The only difference between this embodiment and Embodiment 1 is that the boron source in step four is a borane-ammonia complex. Example 9:

[0028] The only difference between this embodiment and Embodiment 1 is that the calcination temperature in step four is 950 ℃. Example 10:

[0029] The only difference between this embodiment and Embodiment 1 is that the calcination time in step four is 3 hours. Example 11:

[0030] The only difference between this embodiment and Embodiment 1 is that the heating rate in step four is 3 °C / min.

[0031] Comparative Example 1:

[0032] This comparative example uses 20 wt% commercial Pt / C as a control.

[0033] Comparative Example 2:

[0034] The only difference between this comparative example and Example 1 is that thiourea was not added in step one, and step four was not performed. The resulting nitrogen-doped carbon-based metal catalyst is labeled NC.

[0035] Comparative Example 3:

[0036] The only difference between this comparative example and Example 1 is that step four is omitted, and the resulting nitrogen and sulfur co-doped carbon-based metal-free catalyst is labeled as NCS.

[0037] Comparative Example 4:

[0038] The only difference between this comparative example and Example 1 is that the mass ratio of black powder to boric acid in step four is 1:0.5, and the final comparative example 4 is labeled NCSB-2.

[0039] The oxygen reduction electrocatalytic performance test of the nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst of this invention: Weigh 5 mg of the catalyst obtained in Example 1 and place it in a 1.5 mL centrifuge tube. Add 960 μL of isopropanol solution and 40 μL of Nafion solution with a mass concentration of 5 wt%. Sonicate for one hour to obtain a uniformly dispersed catalyst suspension.

[0040] 12 μL of the uniformly dispersed suspension was drop-coated onto a rotating disk electrode and allowed to air dry at room temperature.

[0041] All electrochemical tests in this invention were performed using a Shanghai Chenhua CHI 760E electrochemical workstation, employing a standard three-electrode system. The working electrode was a rotating disk electrode, the reference electrode was an Ag / AgCl electrode, the counter electrode was a carbon rod, and the electrolyte was 0.1 mol / L O2 saturated electrolyte. -1 KOH solution. For example... Figure 3The ORR linear sweep voltammetric curves of the catalysts obtained in Example 1 and Comparative Examples 1-4 are shown. The onset potential and half-wave potential of the nitrogen-sulfur-boron co-doped carbon-based metal-free catalyst reached 1.00 V and 0.91 V, respectively, which are higher than those of commercial Pt / C and significantly higher than those of other comparative catalysts, showing its excellent oxygen reduction activity.

[0042] The application of the nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst of this invention in the performance testing of zinc-air battery cathodes: 120 μL of a catalyst suspension prepared from the catalyst obtained in Example 1, isopropanol solution, and Nafion solution was drop-coated onto carbon paper as an air cathode, with a zinc sheet as the anode and a 6 mol / L electrolyte. -1 KOH and 0.2 mol / L -1 Zinc acetate solution. For example... Figure 4 The figures show the polarization curves and power density curves of the catalysts obtained in Examples 1 and Comparative Examples 1-3 as air cathodes in zinc-air batteries. As can be seen from the figures, the polarization curves and power densities of the nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst obtained in Example 1 are significantly better than those of commercial Pt / C and other comparative samples. This demonstrates that the nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst of the present invention exhibits excellent battery performance when used as an air cathode in zinc-air batteries and has good development prospects.

[0043] This application utilizes chemical vapor deposition to prepare a nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst. This catalyst exhibits excellent catalytic activity in the oxygen reduction reaction, outperforming commercial Pt / C and other comparative catalysts. When applied as an air cathode in a zinc-air battery, it demonstrates superior battery performance.

Claims

1. A nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst, characterized in that: This nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst was prepared by the following method: Step 1: Dissolve the zinc salt and sulfur-containing precursor in methanol, with a molar ratio of zinc ions to sulfur of 1:1 to 1:10, to obtain solution 1. Dissolve 2-methylimidazole in methanol to obtain solution 2. Step 2: Add solution 2 to solution 1, with a molar ratio of zinc ions to 2-methylimidazole of 1:4 to 1:10, sonicate, and then let stand. Step 3: After centrifuging and drying the precipitate obtained in Step 2, calcine it in an inert atmosphere to obtain a black powder. The calcination temperature is 800~1500℃, the calcination time is 1~8 hours, the heating rate during calcination is 1~30℃ / min, and the inert gas used is 99.999% Ar or N. 2； Step 4: Place the black powder obtained in Step 3 and the boron source in a ceramic boat at the lower and upper air inlets of a tube furnace, respectively. The mass ratio of the black powder to the boron source is 1:1 to 1:

20. Calcinate in an inert atmosphere to obtain the dodecahedral catalyst NCSB-1. The calcination temperature is 400 to 1500℃, the calcination time is 0.5 to 10 hours, the heating rate during calcination is 1 to 30℃ / min, and the inert gas used is 99.999% Ar or N2.

2. The nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst according to claim 1, characterized in that: In step one, the zinc salt is zinc nitrate hexahydrate; the sulfur-containing precursor is one of thiourea, sodium thiosulfate, ammonium sulfate, sublimed sulfur, thioacetamide, dimethylamine sulfide, and potassium thiocyanate.

3. The nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst according to claim 2, characterized in that: In step two, the ultrasound time is 0.2 to 8 hours, and the settling time is 24 to 96 hours.

4. The nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst according to claim 3, characterized in that: In step four, the boron source is one of the following: boric acid, borane amino complex, sodium borohydride, sodium tetraborate, metaboric acid, sodium metaborate, and boron oxide.

5. The application of the nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst of claim 4, characterized in that: The nitrogen, sulfur, and boron co-doped carbon-based metal-free catalyst is used as an air cathode in the oxygen reduction reaction of a zinc-air battery.

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