Preparation of boron-modified metal-nitrogen-carbon electrocatalyst with both durability and activity and application thereof in fuel cell

Abstract

The application relates to preparation of a boron-modified metal-nitrogen-carbon electrocatalyst with durability and activity and application of the electrocatalyst in fuel cells, and belongs to the field of fuel cell electrocatalyst materials. The preparation method is as follows: PEG-PPG-PEG is used as a carbon source, self-assembled with high-iron protoporphyrin IX chloride, dried to obtain a composite mixture, an ammonia borane complex is introduced as a boron source, and the product is pyrolyzed under argon to obtain BN-Fe-Nx / CNCs. The boron-modified metal-nitrogen-carbon electrocatalyst prepared by the method has the advantages of simple operation, fewer processes, less equipment investment, good repeatability, convenience in solving the problem of large-scale production, and new selection of carriers for noble metal electrocatalysts such as platinum, ruthenium, palladium and gold.

Description

Technical Field

[0001] This invention relates to the preparation of a boron-modified metal-nitrogen-carbon electrocatalyst that combines durability and activity, and its application in fuel cells, belonging to the field of fuel cell electrocatalyst materials. Background Technology

[0002] With the rapid development of the Industrial Revolution, the crisis of fossil fuel shortages is impacting human production and life, giving rise to renewable energy sources such as fuel cells, metal-air batteries, and flow batteries. The oxygen reduction reaction (ORR) plays a crucial role in these new energy devices. Platinum-based catalysts are considered the best OCR electrocatalysts, but their scarcity, high recovery costs, and poor durability hinder their large-scale commercial application. Therefore, the rational design of a low-cost and abundant OCR electrocatalyst is urgently needed.

[0003] Transition metal-nitrogen-carbon (MNC) compounds are a new class of catalytic materials with unique chemical and physical properties. In recent years, the application of MNC catalysts in electrochemical reactions has become an emerging research field, especially those containing transition metal nitrogen (MN). X MNC-type catalysts with an iron-carbon structure are considered the most likely replacements for commercially available Pt / C catalysts as electrocatalysts for oxygen reduction reactions. In particular, Fe-NC catalysts are considered the most likely replacements for noble metal platinum-based electrocatalysts, as iron resources are abundant and readily available compared to other transition metals (such as cobalt, nickel, copper, and manganese). However, under acidic conditions, both transition metals and carbon-based supports are easily corroded, thus reducing their catalytic activity.

[0004] Boron (B) is a class of elements that are more corrosion-resistant than carbon, especially boron nitride (BN), which is more corrosion-resistant than carbon materials. Moreover, boron nitride and carbon have similar atomic arrangements, allowing it to be well incorporated into carbon matrices. However, boron nitride (especially hexagonal boron nitride) has lower electrical conductivity than carbon materials, and excessive introduction can be counterproductive. Summary of the Invention

[0005] In order to find alternative non-precious metal electrocatalysts and completely get rid of dependence on imported products, and to select mature commercial raw materials from a cost perspective, the appropriate introduction of boron nitride can maintain the protection of the electrocatalyst itself without affecting its performance. By adjusting the ratio of non-metallic element boron to the self-assembled metal-nitrogen-carbon electrocatalyst, the performance and durability of the electrocatalyst can be optimized. This invention designs a boron-modified metal-nitrogen-carbon electrocatalyst with simple process, self-assembly, which takes into account both durability and activity, as well as its preparation method and application.

[0006] The first objective of this invention is to provide a method for preparing a boron-modified metal-nitrogen-carbon electrocatalyst that balances durability and activity.

[0007] A method for preparing a boron-modified metal-nitrogen-carbon electrocatalyst that balances durability and activity includes the following steps:

[0008] (1) Place poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) in a beaker, then add zinc chloride (ZnCl2), add mixed solvent, and sonicate for 1-30 min until the solution becomes clear, and record it as A; separately take potassium hydroxide (KOH), ferric protoporphyrin IX chloride, boron compound and add water, sonicate for 1-30 min until the solution turns dark green, and record it as B. Slowly pour B into A to form a dark green viscous precipitate, and then rotary evaporate at 50-100℃ for 1-12 h to obtain a mixture of intermediate product micelles and dark green precipitate;

[0009] (2) The dark green mixture was carbonized under argon conditions. The resulting product was washed, dried and ground to obtain boron-modified metal nitrogen carbon (B-Fe-Nx / CNCs) powder for later use.

[0010] The boron compound is boric acid, sodium borohydride, ammonia borane complex, triethylamine borane, trimethylamine borane, dimethylaminomethylborane, dicyclohexylamine borane, or methylborane-tert-butylamine complex; the mixed solvent is a mixture of water and an organic solvent; the ratio of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) to organic solvent and water is 1-1000 mg: 1-100 mL: 1-100 mL, preferably 10-200 mg: 10-50 mL: 10-50 mL, more preferably 50-200 mg: 10-50 mL: 10-50 mL, and even more preferably 100 mg: 25 mL: 25 mL; poly(ethylene glycol) The mass ratio of the following compounds is 1-1000:1-500:1-500:1-500:1-500:1-100, preferably 10-200:10-100:10-100:10-100:10-100, more preferably 50-200:10-50:10-50:10-50:10-50:10-50, and even more preferably 100:40:30.8:20:10.

[0011] Furthermore, the organic solvent is methanol, ethanol, isopropanol, dimethylformamide, or diethylene glycol dimethyl ether, preferably methanol.

[0012] Furthermore, the mixed solvent is a mixture of water and methanol, ethanol, isopropanol, dimethylformamide or diethylene glycol dimethyl ether, preferably water and methanol.

[0013] Furthermore, the volume ratio of water in A to water in B is 1-100:1-100 (e.g., 1-100 mL:1-100 mL), preferably 5:1 (e.g., 50 mL:10 mL).

[0014] Further, the volume ratio of water to organic solvent is 1-100:1-100 (e.g., 1-100 mL:1-100 mL), preferably 1:1 (e.g., 50 mL:50 mL).

[0015] Furthermore, the number-average molecular weight Mn of the poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) is 1000-60000 g / mol.

[0016] Further, in step (1), the carbonization conditions of the boron-modified ferrous metallic nitrogen-carbon (B-Fe-Nx / CNCs) electrocatalyst are as follows: under an argon atmosphere, the temperature is increased to 400-1000℃ at a heating rate of 1℃ / min to 10℃ / min, held for 1-6 hours, and then cooled to room temperature with the furnace, denoted as B-Fe-Nx / CNCs-m (where m is the mass of the boron compound). Preferably, the carbonization conditions of the present invention are as follows: under an argon atmosphere, the temperature is increased to 700-900℃ at a heating rate of 5℃ / min, held for 2-6 hours, and then cooled to room temperature with the furnace, denoted as BN-Fe-Nx / CNCs-mT (where T is the holding temperature). Most preferably, the carbonization conditions are as follows: under an argon atmosphere, the temperature is increased to 800℃ at a heating rate of 5℃ / min, and held for 2 hours.

[0017] Further, in step (2), the washing is an acidic washing activation. The obtained product is soaked in 1-8 mol / L hydrochloric acid (HCl) solution for 1-12 hours, then centrifuged with deionized water until neutral, and then washed with anhydrous ethanol by centrifugation. The centrifugation conditions are: centrifugation at 5000 r / min-10000 r / min for 2-10 minutes. Preferably, the acidic washing activation of the present invention is as follows: the obtained product is soaked in 1-8 mol / L HCl solution, centrifuged with deionized water at 8000 r / min for 5 minutes, centrifuged repeatedly until neutral, and then washed by centrifugation with anhydrous ethanol at 8000 r / min for 5 minutes. Further, the present invention preferably uses a 3 mol / L HCl solution.

[0018] Furthermore, in step (2), the drying conditions after washing are: drying at 50-100℃ for 12-36 hours, which can be done using a forced-air drying oven.

[0019] Another object of the present invention is to provide a boron-modified metal-nitrogen-carbon electrocatalyst prepared by the above method that combines durability and activity. The boron-modified metal-nitrogen-carbon electrocatalyst of the present invention, which combines durability and activity, has an oval structure and a specific surface area of ​​100–3000 m². 2 g -1 Preferably, the specific surface area is 1000-2000 m². 2 g -1 More preferably, the specific surface area is 1346 m². 2 g -1 .

[0020] The boron-modified metal-nitrogen-carbon electrocatalyst of the present invention, which balances durability and activity, shows a significant improvement in both performance and durability after modification with boron.

[0021] Another object of the present invention is to provide the application of the above-mentioned boron-modified metal-nitrogen-carbon electrocatalyst as a cathode catalyst material and catalyst support material for fuel cells.

[0022] This invention uses a boron compound (e.g., an ammonia-borane complex (NH3-BH3)) as a boron source. Under high temperature conditions, it can decompose to release hydrogen gas, which protects the aggregation of metallic Fe. The decomposed ammonia gas is further doped with nitrogen to obtain more Fe-NC structures. The resulting mixture powder is carbonized under argon conditions. The product is then washed, dried, and ground to obtain the final product.

[0023] This invention carefully combines boron compounds (such as ammoniaborane complexes) with metal-nitrogen-carbon materials. Some boron and nitrogen coordinate with iron to form iron-boron bonds or iron-nitrogen bonds, thereby improving activity. The original Fe-Nx active sites and carbon support are protected by boron and nitrogen modification. Without affecting conductivity, boron and nitrogen will produce some hexagonal boron nitride at high temperatures, which prevents the metal-nitrogen-carbon electrocatalyst from being poisoned. The constructed boron-modified metal-nitrogen-carbon electrocatalyst makes up for the lack of catalyst durability of transition metals under acidic conditions.

[0024] This invention utilizes an ammonia-borane complex containing significant amounts of nitrogen and boron. Boron nitride is a highly corrosion-resistant protective material, with some hexagonal boron nitride exhibiting even superior corrosion resistance compared to regular boron nitride. A boron-modified metal-nitrogen-carbon electrocatalyst (BN-Fe-Nx / CNCs) was creatively designed after a one-step pyrolysis. The presence of hexagonal boron nitride in this boron-modified metal-nitrogen-carbon electrocatalyst forms a protective layer on the carbon support surface. During durability testing, this layer prevents the carbon support from poisoning, indirectly protecting the metal-nitrogen-carbon active sites and thus influencing the overall oxygen reduction activity of the electrocatalyst. The boron-modified metal-nitrogen-carbon electrocatalyst also demonstrated excellent performance and long-term stability as an oxygen reduction electrocatalyst for fuel cell cathodes.

[0025] The beneficial effects of this invention are as follows: the metal-nitrogen-carbon electrocatalyst material prepared using the method described herein exhibits excellent electrocatalytic performance. The introduction of boron not only does not affect its electrocatalytic activity, but on the contrary, alters the local coordination environment, protecting the Fe-Nx active sites. Boron nitride encapsulates the carbon matrix, significantly improving activity while maintaining durability through an inexpensive material. Furthermore, it can also be used as a support for commercially available platinum-based electrocatalysts. The method for preparing boron-modified metal-nitrogen-carbon electrocatalysts according to this invention is simple to operate, involves fewer processes, requires less equipment investment, and has good reproducibility, facilitating large-scale production and providing a new option for supports of precious metal electrocatalysts such as platinum, palladium, and gold. Attached Figure Description

[0026] Figure 1 (a) is a scanning electron microscope (SEM) image (scale bar is 400 nm) of BN-Fe-Nx / CNCs-10 prepared in Example 1 of the present invention. Figure 1 Image (b) is a scanning electron microscope (SEM) image (scale bar 2 μm) of BN-Fe-Nx / CNCs-10 prepared in Example 1 of this invention.

[0027] Figure 2 (a) shows the XRD patterns of the BN-Fe-Nx / CNCs-10 electrocatalysts prepared in Example 1 and Comparative Example 1. Figure 2 (b) shows the Raman spectra of the BN-Fe-Nx / CNCs-10 electrocatalysts prepared in Example 1 and Comparative Example 1.

[0028] Figure 3 (a) shows the nitrogen adsorption-desorption curves of the electrocatalysts of BN-Fe-Nx / CNCs-10 prepared in Example 1 and Comparative Example 1 and BN-CNCs-10 prepared in Comparative Example 1. Figure 4(b) shows the pore size distribution curves of Example 1 and Comparative Example 1.

[0029] Figure 4 In the middle (a) to (d), the XPS total spectrum, B1s, N1s and Fe2p spectra of the BN-Fe-Nx / CNCs-10 electrocatalyst prepared in Example 1 are respectively.

[0030] Figure 5 (a) shows the polarization curves of the boron-modified metal-nitrogen-carbon electrocatalyst materials prepared in Examples 1-6 and Comparative Example 2 under acidic conditions at 1600 rpm. Figure 5 (b) shows the durability test of the boron-modified metal-nitrogen-carbon electrocatalysts BN-Fe-Nx / CNCs-10 and 20wt% Pt / C prepared in Example 1 of this invention under acidic conditions.

[0031] Figure 6 In Figure (a), the cyclic voltammetry curves (nitrogen and oxygen) of the BN-Fe-Nx / CNCs-10 electrocatalysts prepared in Example 1 and Comparative Example 1 are shown. Figure 6 (b) shows the polarization curves of BN-Fe-Nx / CNCs-10 prepared in Example 1 of the present invention, BN-CNCs-10 prepared in Comparative Example 1, and commercial 20wt% Pt / C at 1600 rpm under acidic conditions.

[0032] Figure 7 In Example 1 of this invention, boron-modified metal-nitrogen-carbon electrocatalysts with different loadings (0.6-1.4 mg / cm³) are shown in Figure (a). 2 Polarization curves under acidic conditions; Figure 7 (b) shows the polarization curves and the number of transferred electrons of the boron-modified metal-nitrogen-carbon electrocatalyst material prepared in Example 1 of this invention under different rotation speeds in acidic conditions.

[0033] Figure 8 (a) shows the cyclic voltammetry curve changes of the BN-Fe-Nx / CNCs-10 electrocatalyst prepared in Example 1 of this invention during the durability test under acidic conditions; Figure 8 Figure (b) shows the polarization curve changes of the BN-Fe-Nx / CNCs-10 electrocatalyst prepared in Example 1 of this invention during the durability test under acidic conditions. Detailed Implementation

[0034] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but are not intended to limit the invention in any way.

[0035] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0036] Example 1

[0037] 1) Take 100 mg of polyethylene glycol (PEG-PPG-PEG, number average molecular weight Mn is 12600 g / mol) and 40 mg of ZnCl2 and put them into a 250 mL beaker. Add 50 mL of deionized water and 50 mL of methanol. Sonicate for 5 min until the solution is clear and transparent. Record this solution as A.

[0038] 2) Take another 30.8 mg KOH, 20 mg ferric protoporphyrin IX chloride and 10 mg ammonia borane complex (CAS No.: 13774-81-7, Aladdin) into a 20 mL sample bottle, add 10 mL deionized water, sonicate for 5 min, and the solution turns dark green, which is recorded as B.

[0039] 3) Slowly pour B into A, sonicate for 5 minutes, and dry in a forced-air drying oven at 60°C for 12 hours to obtain a mixture of dark green powder and thin film.

[0040] 4) The mixture was carbonized in a tube furnace with argon gas. The carbonization procedure was as follows: the temperature was increased from room temperature to 800℃ at a rate of 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace. The mixture was then removed and ground. First, it was soaked in 3mol / L HCl solution, centrifuged with deionized water at 8000r / min for 5 minutes, and centrifuged repeatedly until neutral. Then, it was washed by centrifuging with anhydrous ethanol at 8000r / min for 5 minutes. It was then dried in a forced-air drying oven at 60℃ for 12 hours and ground. The mixture was labeled as BN-Fe-Nx / CNCs-10.

[0041] 5) The catalyst was tested for RDE (rotating disk electrode) performance in a standard three-electrode electrochemical cell under acidic conditions (0.1M HClO4). A glassy carbon electrode with the catalyst droplets was used as the working electrode, a graphite rod as the counter electrode, and saturated calomel as the reference electrode in the acidic system. The catalyst loading on the electrode provided in Example 1 was 0.6 mg / cm³. 2 All potentials in this invention are Reynolds-Hemisphere (RHE) potentials. A 20 wt% Pt / C electrocatalyst was used as a control with a loading of 10 μg. Pt ·cm -2 The test was conducted at 25°C in a 0.1M HClO4 aqueous solution saturated with N2 or O2. The positive scan rate was 50 mV·s. -1 Under the conditions specified, the cyclic voltammetry (CV) curves of the catalyst were tested. The rotational speed was 1600 rpm and the positive scan rate was 10 mV·s.-1 At that time, the ORR polarization curve was tested. The electrochemical testing conditions of the catalyst in Examples 2-6 and Comparative Examples 1-2 were the same as those in Example 1.

[0042] Example 2

[0043] 1) Take 100 mg of polyethylene glycol (PEG-PPG-PEG, number average molecular weight Mn is 12600 g / mol) and 40 mg of ZnCl2 and put them into a 250 mL beaker. Add 50 mL of deionized water and 50 mL of methanol. Sonicate for 5 min until the solution is clear and transparent. Record this solution as A.

[0044] 2) Take 30.8 mg KOH, 20 mg ferric protoporphyrin IX chloride and 5 mg ammonia borane complex (CAS No.: 13774-81-7, Aladdin) in a 20 mL sample bottle, add 10 mL deionized water, sonicate for 5 min, and the solution will turn dark green, which is recorded as B.

[0045] 3) Slowly pour B into A, sonicate for 5 minutes, and dry in a forced-air drying oven at 60°C for 12 hours to obtain a mixture of dark green powder and thin film.

[0046] 4) The mixture was carbonized in a tube furnace with argon gas. The carbonization procedure was as follows: the temperature was increased from room temperature to 800℃ at a rate of 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace. The mixture was then removed and ground. First, it was soaked in 3mol / L HCl solution, centrifuged with deionized water at 8000r / min for 5 minutes, and centrifuged repeatedly until neutral. Then, it was washed by centrifuging with anhydrous ethanol at 8000r / min for 5 minutes. It was then dried in a forced-air drying oven at 60℃ for 12 hours and ground. The mixture was labeled as BN-Fe-Nx / CNCs-5.

[0047] Example 3

[0048] 1) Take 100 mg of polyethylene glycol (PEG-PPG-PEG, number average molecular weight Mn is 12600 g / mol) and 40 mg of ZnCl2 and put them into a 250 mL beaker. Add 50 mL of deionized water and 50 mL of methanol. Sonicate for 5 min until the solution is clear and transparent. Record this solution as A.

[0049] 2) Take 30.8 mg KOH, 20 mg ferric protoporphyrin IX chloride and 15 mg ammonia borane complex (CAS No.: 13774-81-7, Aladdin) in a 20 mL sample bottle, add 10 mL deionized water, sonicate for 5 min, and the solution turns dark green, which is recorded as B.

[0050] 3) Slowly pour B into A, sonicate for 5 minutes, and dry in a forced-air drying oven at 60°C for 12 hours to obtain a mixture of dark green powder and thin film.

[0051] 4) The mixture was carbonized in a tube furnace with argon gas. The carbonization procedure was as follows: the temperature was increased from room temperature to 800℃ at a rate of 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace. The mixture was then removed and ground. First, it was soaked in 3mol / L HCl solution, centrifuged with deionized water at 8000r / min for 5 minutes, and centrifuged repeatedly until neutral. Then, it was washed by centrifuging with anhydrous ethanol at 8000r / min for 5 minutes. It was then dried in a forced-air drying oven at 60℃ for 12 hours and ground. The mixture was labeled as BN-Fe-Nx / CNCs-15.

[0052] Example 4

[0053] 1) Take 100 mg of polyethylene glycol (PEG-PPG-PEG, number average molecular weight Mn is 12600 g / mol) and 40 mg of ZnCl2 and put them into a 250 mL beaker. Add 50 mL of deionized water and 50 mL of methanol. Sonicate for 5 min until the solution is clear and transparent. Record this solution as A.

[0054] 2) Take 30.8 mg KOH, 20 mg ferric protoporphyrin IX chloride and 20 mg ammonia borane complex (CAS No.: 13774-81-7, Aladdin) into a 20 mL sample bottle, add 10 mL deionized water, sonicate for 5 min, and the solution turns dark green, which is recorded as B.

[0055] 3) Slowly pour B into A, sonicate for 5 minutes, and dry in a forced-air drying oven at 60°C for 12 hours to obtain a mixture of dark green powder and thin film.

[0056] 4) The mixture was carbonized in a tube furnace with argon gas. The carbonization procedure was as follows: the temperature was increased from room temperature to 800℃ at a rate of 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace. The mixture was then removed and ground. First, it was soaked in 3mol / L HCl solution, centrifuged with deionized water at 8000r / min for 5 minutes, and centrifuged repeatedly until neutral. Then, it was washed by centrifuging with anhydrous ethanol at 8000r / min for 5 minutes. It was then dried in a forced-air drying oven at 60℃ for 12 hours and ground. The mixture was labeled as BN-Fe-Nx / CNCs-20.

[0057] Example 5

[0058] 1) Take 100 mg of polyethylene glycol (PEG-PPG-PEG, number average molecular weight Mn is 12600 g / mol) and 40 mg of ZnCl2 and put them into a 250 mL beaker. Add 50 mL of deionized water and 50 mL of methanol. Sonicate for 5 min until the solution is clear and transparent. Record this solution as A.

[0059] 2) Take 30.8 mg KOH, 20 mg ferric protoporphyrin IX chloride and 25 mg ammonia borane complex (CAS No.: 13774-81-7, Aladdin) into a 20 mL sample bottle, add 10 mL deionized water, sonicate for 5 min, and the solution turns dark green, which is recorded as B.

[0060] 3) Slowly pour B into A, sonicate for 5 minutes, and dry in a forced-air drying oven at 60°C for 12 hours to obtain a mixture of dark green powder and thin film.

[0061] 4) The mixture was carbonized in a tube furnace with argon gas. The carbonization procedure was as follows: the temperature was increased from room temperature to 800℃ at a rate of 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace. The mixture was then removed and ground. First, it was soaked in 3mol / L HCl solution, centrifuged with deionized water at 8000r / min for 5 minutes, and centrifuged repeatedly until neutral. Then, it was washed by centrifuging with anhydrous ethanol at 8000r / min for 5 minutes. It was then dried in a forced-air drying oven at 60℃ for 12 hours and ground. The mixture was labeled as BN-Fe-Nx / CNCs-25.

[0062] Example 6

[0063] 1) Take 100 mg of polyethylene glycol (PEG-PPG-PEG, number average molecular weight Mn is 12600 g / mol) and 40 mg of ZnCl2 and put them into a 250 mL beaker. Add 50 mL of deionized water and 50 mL of methanol. Sonicate for 5 min until the solution is clear and transparent. Record this solution as A.

[0064] 2) Take 30.8 mg KOH, 20 mg ferric protoporphyrin IX chloride and 30 mg ammonia borane complex (CAS No.: 13774-81-7, Aladdin) in a 20 mL sample bottle, add 10 mL deionized water, sonicate for 5 min, and the solution turns dark green, which is recorded as B.

[0065] 3) Slowly pour B into A, sonicate for 5 minutes, and dry in a forced-air drying oven at 60°C for 12 hours to obtain a mixture of dark green powder and thin film.

[0066] 4) The mixture was carbonized in a tube furnace with argon gas. The carbonization procedure was as follows: the temperature was increased from room temperature to 800℃ at a rate of 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace. The mixture was then removed and ground. First, it was soaked in 3mol / L HCl solution, centrifuged with deionized water at 8000r / min for 5 minutes, and centrifuged repeatedly until neutral. Then, it was washed by centrifuging with anhydrous ethanol at 8000r / min for 5 minutes. It was then dried in a forced-air drying oven at 60℃ for 12 hours and ground. The mixture was labeled as B-Fe-Nx / CNCs-30.

[0067] Comparative Example 1

[0068] 1) Take 100 mg of polyethylene glycol (PEG-PPG-PEG, number average molecular weight Mn is 12600 g / mol) and 40 mg of ZnCl2 and put them into a 250 mL beaker. Add 50 mL of deionized water and 50 mL of methanol. Sonicate for 5 min until the solution is clear and transparent. Record this solution as A.

[0069] 2) Take another 30.8 mg KOH and 10 mg of ammonia borane complex (CAS No.: 13774-81-7, Aladdin) into a 20 mL sample bottle, add 10 mL of deionized water, sonicate for 5 min, and make the solution dark green, which is recorded as B.

[0070] 3) Slowly pour B into A, sonicate for 5 minutes, and dry in a forced-air drying oven at 60°C for 12 hours to obtain a mixture of dark green powder and thin film.

[0071] 4) The mixture was carbonized in a tube furnace with argon gas. The carbonization procedure was as follows: the temperature was increased from room temperature to 800℃ at a rate of 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace. The mixture was then removed and ground. First, it was soaked in 3mol / L HCl solution, centrifuged with deionized water at 8000r / min for 5 minutes, and centrifuged repeatedly until neutral. Then, it was washed by centrifuging with anhydrous ethanol at 8000r / min for 5 minutes. It was then dried in a forced-air drying oven at 60℃ for 12 hours and ground. The mixture was labeled BN CNCs-10.

[0072] Comparative Example 2

[0073] 1) Take 100 mg of polyethylene glycol (PEG-PPG-PEG, number average molecular weight Mn is 12600 g / mol) and 40 mg of ZnCl2 and put them into a 250 mL beaker. Add 50 mL of deionized water and 50 mL of methanol. Sonicate for 5 min until the solution is clear and transparent. Record this solution as A.

[0074] 2) Take another 30.8 mg KOH and 20 mg ferric protoporphyrin IX chloride into a 20 mL sample bottle, add 10 mL deionized water, sonicate for 5 min, and make the solution dark green, which is recorded as B.

[0075] 3) Slowly pour B into A, sonicate for 5 minutes, and dry in a forced-air drying oven at 60°C for 12 hours to obtain a mixture of dark green powder and thin film.

[0076] 4) The mixture was carbonized in a tube furnace with argon gas. The carbonization procedure was as follows: the temperature was increased from room temperature to 800℃ at a rate of 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace. The mixture was then removed and ground. First, it was soaked in 3mol / L HCl solution, centrifuged with deionized water at 8000r / min for 5 minutes, and centrifuged repeatedly until neutral. Then, it was washed by centrifuging with anhydrous ethanol at 8000r / min for 5 minutes. It was then dried in a forced-air drying oven at 60℃ for 12 hours and ground. The mixture was labeled as BN-Fe-Nx / CNCs-0.

[0077] Example of effectiveness: In order to investigate the morphological characteristics and electrochemical performance of boron-modified metal-nitrogen-carbon electrocatalysts, the prepared products were physically characterized by SEM, XRD, XPS, Raman and other methods, and the products were prepared into electrodes to test the corresponding electrochemical performance.

[0078] Figure 1 Image (a) is a SEM image (scale bar 400 nm) of the BN-Fe-Nx / CNCs-10 catalyst prepared in Example 1. Figure 1 As can be seen from the SEM image in (a), BN-Fe-Nx / CNCs-10 exhibits an ellipsoidal morphology. Figure 1 SEM image (scale bar 2 μm) of the BN-Fe-Nx / CNCs-10 catalyst prepared in Example 1 (b). Figure 1 As can be seen from the SEM image in (b), the morphology of BN-Fe-Nx / CNCs-10 is composed of ellipsoidal packing.

[0079] Figure 2 In Figure (a), the XRD patterns of the BN-Fe-Nx / CNCs-10 electrocatalysts prepared in Example 1 and Comparative Example 1 are shown. The peak positions of Example 1 and Comparative Example 1 are the same. After carbonization at 800℃, there are no metal diffraction peaks. Only the morphology is changed, indicating that the metal may be embedded inside the carbon support or the metal may be dispersed in the carbon support in an atomic-level form. Figure 2 (b) shows the Raman spectra of the BN-Fe-Nx / CNCs-10 electrocatalysts prepared in Example 1 and Comparative Example 1. The D peak appears at 1350 cm⁻¹. -1At this location, the G peak appears at 1580cm. -1 The degree of defect and graphitization of the sample can be determined from the D and G peaks. The Raman spectra of BN-Fe-Nx / CNCs-10 and BN-CNCs-10 are shown in the figure. D and I G The ratios were 0.90 and 1.05, respectively. The graphitization degree of BN-Fe-Nx / CNCs-10 was better than that of BN-CNCs-10, indicating that the carbon cages in the metal iron catalysis part were transformed to the degree of graphitization.

[0080] Figure 3 (a) shows the nitrogen adsorption-desorption curves of the BN-Fe-Nx / CNCs-10 electrocatalysts prepared in Example 1 and Comparative Example 1. The total specific surface area of ​​BN-CNCs-10 is 2641 m². 2 ·g -1 The total specific surface area of ​​BN-Fe-Nx / CNCs-10 is 1346 m². 2 ·g -1 ,in Figure 3 Figure (b) shows the pore size distribution curves of the BN-Fe-Nx / CNCs-10 electrocatalysts prepared in Example 1 and Comparative Example 1. The pore sizes of the samples are all concentrated at 40 nm, indicating they are mesoporous.

[0081] Figure 4 Images (a) through (d) show the XPS full spectrum, B1s, N1s, and Fe2p spectra of the BN-Fe-Nx / CNCs-10 electrocatalyst prepared in Example 1. Figure 4 In (a), Fe, B, and N elements can be clearly observed. Figure 4 (b) is a high-resolution B1s spectrum, from which the BN(h-BN) form can be obtained. Figure 4 (c) is a high-resolution N1s spectrum, from which nitrogen can be seen to exist in the forms of Fe-N, graphitic nitrogen, pyrrole nitrogen, pyridine nitrogen and a small amount of nitrogen oxide. Figure 4 The middle (d) image shows the high-resolution Fe2p spectrum.

[0082] Figure 5 Image (a) shows the polarization curves of the boron-modified metal-nitrogen-carbon electrocatalysts prepared in Examples 1-6 and Comparative Example 2 under acidic conditions at 1600 rpm; from Figure 5 As can be seen in (a), in the polarization curves of electrocatalyst materials with different boron precursor ratios in 0.1M HClO4 aqueous solution at 1600 rpm, the electrochemical performance first increases and then decreases with the increase of boron precursor ratio. BN-Fe-Nx / CNCs-10 exhibits the best performance: good onset potential and half-wave potential. Figure 5 Image (b) shows a comparison of the polarization curves of the BN-CNCs-10 electrocatalyst prepared in Example 1 of this invention and 20wt% Pt / C under acidic conditions in a durability test; from Figure 5 As can be seen in (b), after 3000 cycles of durability testing in 0.1M HClO4 aqueous solution, the half-wave potential of BN-Fe-Nx / CNCs-10 decreased by 18mV; the half-wave potential of 20wt%Pt / C decreased by 40mV.

[0083] Figure 6 (a) shows the cyclic voltammetry curves (nitrogen and oxygen) of the BN-Fe-Nx / CNCs-10 electrocatalyst prepared in Example 1 and the BN-CNCs-10 electrocatalyst prepared in Comparative Example 1 under acidic conditions. In the oxygen-saturated 0.1M HClO4 aqueous solution, the electrocatalysts of Example 1 and Comparative Example 1 showed obvious oxygen reduction peaks, with Example 1 located between 0.6-0.8V and Comparative Example 1 located between 0.1-0.3V. Figure 6 (b) shows the polarization curves of Example 1, Comparative Example 1 and commercial 20wt% Pt / C at 1600 rpm under acidic conditions, of which the optimal one is BN-Fe-Nx / CNCs-10, with a half-wave potential of 0.83V.

[0084] Figure 7 In Example 1 of this invention, boron-modified metal-nitrogen-carbon electrocatalysts with different loadings (0.6-1.4 mg / cm³) are shown in Figure (a). 2 Polarization curves under acidic conditions; from Figure 7 As can be seen in (a), the CV curve of the BN-Fe-Nx / CNCs-10 electrocatalyst material is slightly attenuated in 0.1M HClO4 aqueous solution. Figure 7 (b) shows the polarization curves and the number of transferred electrons of the boron-modified metal-nitrogen-carbon electrocatalyst material prepared in Example 1 of the present invention under different rotation speeds under acidic conditions. The number of transferred electrons is close to four electrons, which is beneficial to the four-electron pathway of oxygen reduction reaction.

[0085] Figure 8 In Figure (a), the cyclic voltammetry curve of the BN-Fe-Nx / CNCs-10 electrocatalyst prepared in Example 1 of this invention is shown during the durability test under acidic conditions, and the limiting current density shows a decreasing trend. Figure 8 Figure (b) shows the polarization curve changes of the BN-Fe-Nx / CNCs-10 electrocatalyst prepared in Example 1 of this invention during the durability test under acidic conditions. Its half-wave potential and onset potential show a decreasing trend.

Claims

1. A method for preparing a boron-modified metal-nitrogen-carbon electrocatalyst that balances durability and activity, characterized in that: Includes the following steps: (1) Mix PEG-PPG-PEG and zinc chloride, add mixed solvent, sonicate for 1-30 min, and record as A; separately take potassium hydroxide, ferric protoporphyrin IX chloride and boron compound, add water, sonicate for 1-30 min and record as B; pour B into A, and rotary evaporate at 50-100℃ for 1-12 h to obtain the mixture; (2) The mixture was carbonized under argon conditions. The resulting product was washed, dried and ground to obtain a black metallic nitrogen carbon powder. The boron compound is boric acid, sodium borohydride, ammonia borane complex, triethylamine borane, trimethylamine borane, dimethylaminomethylborane, dicyclohexylamine borane, or methylborane-tert-butylamine complex; the mixed solvent is a mixture of water and an organic solvent; the ratio of PEG-PPG-PEG to organic solvent to water is 1-1000 mg: 1-100 mL: 1-100 mL; the mass ratio of PEG-PPG-PEG, zinc chloride, potassium hydroxide, ferric protoporphyrin IX chloride, and boron compound is 50-200 mg: 10-50 mg: 10-50 mg: 10-50 mg: 10-50 mg; In step (2), the carbonization conditions are: under an argon atmosphere, the temperature is increased to 800°C at a heating rate of 5°C / min, held for 2 hours, and then cooled to room temperature with the furnace. The boron-modified metal-nitrogen-carbon electrocatalyst has an egg-shaped structure.

2. The method according to claim 1, characterized in that, The organic solvent is methanol, ethanol, isopropanol, dimethylformamide, or diethylene glycol dimethyl ether.

3. The method according to claim 1, characterized in that, The volume ratio of water to organic solvent is 1:

1.

4. The method according to claim 1, characterized in that: The number-average molecular weight (Mn) of the PEG-PPG-PEG is 1000–60000 g / mol.

5. The method according to claim 1, characterized in that: In step (2), the washing process involves soaking the obtained product in a 1-8 mol / L hydrochloric acid solution for 1-12 hours, then centrifuging it with deionized water until neutral, and finally centrifuging it with anhydrous ethanol.

6. The method according to claim 5, characterized in that: The centrifugation conditions are: centrifugation at 5000 r / min to 10000 r / min for 2 to 10 minutes.

7. A boron-modified metal-nitrogen-carbon electrocatalyst that combines durability and activity, prepared by the method according to any one of claims 1 to 6.

8. The boron-modified metal-nitrogen-carbon electrocatalyst that combines durability and activity according to claim 7, characterized in that: Specific surface area of ​​100–3000 m² 2 g -1 .

9. The application of the boron-modified metal-nitrogen-carbon electrocatalyst of claim 7 or 8, which combines durability and activity, as a cathode electrocatalyst material and catalyst support material for fuel cells.

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