CN115763845A - Preparation method of chromium-based inorganic substance coupled transition metal nitrogen-doped carbon catalyst - Google Patents

Abstract

The invention discloses a preparation method of a chromium-based inorganic substance coupling transition metal nitrogen-doped carbon catalyst, which belongs to the field of electrocatalysis. The method starts with the configuration of the metal M-bipyridine solution, and then sequentially adds sodium chloride, chromium salt and organic ammonium salt to the above solution and stirs to dissolve the solid and evaporate to dryness to obtain a mixed powder; Acid washing-suction filtration-drying to obtain the catalyst. It has the following advantages: the chromium salt inorganic carrier is introduced into the M-N-C atomically dispersed catalyst by the molten salt template method to replace the conventional carbon carrier, and the method is applicable to a variety of metal-nitrogen co-doped carbon catalysts (such as Fe, Cu, Ni, etc.); the catalyst is an ultra-thin two-dimensional sheet composed of interconnected nanocrystals, which can effectively improve the mass transfer capacity; the introduction of chromium-based inorganic salts can improve Faradaic efficiency, catalytic activity, and high current and long-term working conditions The durability is significantly better than that of commercial platinum carbon catalysts and transition metal nitrogen doped carbons.

Description

Preparation method of a chromium-based inorganic substance coupling transition metal nitrogen-doped carbon catalyst

technical field

The invention belongs to the field of new energy materials. Specifically, a two-dimensional sheet-like chromium-based inorganic substance is used as a carrier to couple transition metal nitrogen-doped carbon-type atomic-level dispersion materials (M-N-C, M being Fe, Co, Cu and Ni. One or several) are prepared into composite catalysts, which are used in fuel cells, cathode oxygen reduction reaction (ORR) of metal-air batteries, and oxygen evolution reaction (OER) of electrolyzed water.

Background technique

Electrocatalyst is one of the core components of many new energy conversion devices such as fuel cells, metal-air batteries, and electrolytic water projects. At present, electrocatalysts are still dominated by noble metal catalytic materials, such as Pt, Pd, Ru, and Ir, which are the most advanced oxygen electrode catalysts. However, its high price and limited reserves have greatly restricted the development of new energy industries. Therefore, it is necessary to develop non-precious metal catalysts with high catalytic performance to replace noble metal catalysts.

In PGM-free catalysts, transition metal nitrogen-doped carbon-type atomically dispersed materials (MNCs), that is, atomically dispersed and nitrogen-coordinated MN _x sites embedded in carbon planes, play an important role in oxygen reduction, oxygen evolution ( OER) and carbon dioxide reduction (CO ₂ RR) and other fields have shown good performance, showing a good application prospect. The extremely high surface-to-volume ratio of MNCs enhances the catalytic efficiency per atom, improves the uniformity of active sites, and enables tuning of the guest environment, all of which are not only attractive for industrial applications but also provide insight into atomic-level catalytic mechanisms. Also attractive. Despite their tremendous progress in terms of activity and site structure, improved durability is urgently needed due to poor understanding of their degradation mechanisms during operation. Further research and improvement of MNC catalysts are still needed to facilitate practical applications, especially at high currents, and the long-term stability of catalysts in harsh battery tests.

Contents of the invention

In view of the lack of catalytic activity and stability of the existing transition metal nitrogen-doped carbon catalyst M-N-C (M is one or more of Fe, Co, Cu and Ni), a two-dimensional sheet-like chromium-based inorganic material is provided As a support carrier coupled with M-N-C as a catalyst, the catalytic durability of the obtained catalyst is significantly higher than that of the traditional M-N-C catalyst and the latest commercial 20%Pt/C catalyst.

In order to achieve the above object, the technical scheme that the present invention takes is as follows:

A preparation method of a chromium-based inorganic substance coupling transition metal nitrogen-doped carbon catalyst, the method steps are:

Step 1: Preparation of metal M-bipyridine solution:

At room temperature, weigh the metal M salt and bipyridine and dissolve them in ultrapure water respectively. After they are completely dissolved, mix the two solutions to obtain an orange-yellow solution. Stir at room temperature to fully coordinate the growth of M ions and bipyridine;

Step 2: Preparation of M-Cr-organic ammonium salt mixed precursor:

Add sodium chloride, chromium salt and organic ammonium salt to the orange-yellow solution obtained in step 1 and stir to dissolve the solid completely; place the above solution on a heating platform, and remove the water in the solution by rotary evaporation to obtain The solid mixture is placed in a vacuum oven, heated and dried under vacuum to remove the remaining water, and obtains the mixed precursor of M-Cr-organic ammonium salt;

Step 3: Preparation of M-N-C composite catalyst coupled with chromium-based inorganic substances:

Put the precursor obtained in step 2 into a mortar and grind it thoroughly, and then put it into a tube furnace for calcination under a protective atmosphere; the calcined product is dispersed in an aqueous solution, and the sodium chloride template is removed by washing with water several times; in order to remove possible Existing metal M clusters, disperse the template-removed product into dilute H ₂ SO ₄ aqueous solution, and keep stirring at 80°C for 5 hours, wash with water-suction-filter-vacuum dry to obtain chromium-based inorganic compound coupling Transition metal nitrogen doped carbon catalysts.

Further, in step 1, the molar ratio of the metal M salt to bipyridyl is 1:1-4.

Further, in step one, the metal M salt is ferric nitrate, ferric chloride, ferric acetate, ferrous nitrate, ferrous chloride, ferrous acetate, cobalt nitrate, cobalt chloride, cobalt acetate, copper nitrate, chlorine One or more of copper chloride, copper acetate, nickel nitrate, nickel chloride, and nickel acetate, and the bipyridine is 2,2'-bipyridine or 4,4'-bipyridine.

Further, in step 2, the input amount of the sodium chloride is determined according to the volume of the M-bipyridine solution, each milliliter of the solution corresponds to 0.5 g of sodium chloride, and the molar ratio of the chromium salt to the metal M salt is 1 to 8 :1, the mass ratio of the organic ammonium salt to the chromium salt is 3:1.

Further, in step 2, the chromium salt is one of chromium chloride, chromium sulfate, and chromium nitrate, and the organic ammonium salt is one of urea, melamine, dicyandiamide, and ammonium citrate.

Further, in step 3, the protective atmosphere is Ar or N ₂ , the calcination temperature is 650-800°C, the time is 1-3h, and the heating rate is 2-10°C/min.

A chromium-based inorganic substance coupled transition metal nitrogen-doped carbon catalyst prepared by the above method.

An application of a chromium-based inorganic substance coupled transition metal nitrogen-doped carbon catalyst prepared by the above method in a fuel cell, a cathode oxygen reduction reaction (ORR) of a metal-air battery, and an oxygen evolution reaction (OER) of electrolyzed water.

The beneficial effect of the present invention relative to prior art is:

(1) The present invention can introduce the chromium-based inorganic carrier into the M-N-C atomically dispersed catalyst to replace the conventional carbon carrier through a simple and effective molten salt template method, thereby synthesizing a variety of ultra-stable catalysts with different components and structures. The choice of ammonium nitrogen salt controls the form of chromium-based inorganic substances, and the nanoscale of the catalyst can also be controlled by changing the input amount of sodium chloride template. The method is green, mild and simple, and has great versatility.

(2) The chromium-based inorganic substance coupling M-N-C catalyst of the present invention is an ultrathin two-dimensional sheet structure composed of many interconnected nanocrystals. This two-dimensional structure helps to fully contact the active sites and reactants during the catalytic process. The open structure on both sides of the nanosheet can also effectively improve the efficiency of the mass transfer process and simplify the transportation of reaction intermediates and products. . Due to the large number of pores between the crystals, the electrolyte and ions are allowed to transport through the flakes, which can also greatly improve the mass transfer capacity of the catalyst.

(3) The chromium-based inorganic carrier introduced in the present invention can improve the degree of graphitization of M-N-C and enhance the conductivity of the catalyst. The introduction of chromium-based inorganic substances can also induce electron spin polarization in the carbon layer where M-N-C is located, improve catalytic selectivity and Faradaic efficiency, and reduce the generation of by-products. Chromium-based inorganic substances are more thermodynamic and corrosion-resistant than carbon supports, ensuring the long-term stability of the catalyst under high current and harsh battery tests.

In summary, the catalyst of the present invention is an ultrathin two-dimensional sheet composed of many interconnected nanocrystals. The introduction of chromium-based inorganic carrier into the M-N-C atomically dispersed catalyst aims to replace the conventional carbon support, improve the degree of graphitization of M-N-C, improve catalytic selectivity and Faradaic efficiency, and improve the durability of the catalyst under high current and long-term working conditions sex.

Description of drawings

Fig. 1 is the flow chart that the embodiment of the present invention 1-3 prepares;

Fig. 2 is the SEM image of CoCN@Cr ₂ O ₃ prepared in Example 1 of the present invention;

Fig. 3 is the SEM image of FeCN@Cr ₂ O ₃ prepared in Example 2 of the present invention;

Figure 4 is a SEM image of NiCN@CrN prepared in Example 3 of the present invention;

Figure 5 is a TEM image of CoCN@Cr ₂ O ₃ prepared in Example 1 of the present invention;

Fig. 6 is the HRTEM diagram of CoCN@Cr ₂ O ₃ prepared in Example 1 of the present invention;

Fig. 7 is the XPS spectrum of CoCN@Cr ₂ O ₃ prepared in Example 1 of the present invention and CoCN prepared in Comparative Example 3;

Figure 8 is the XPS spectrum of CoCN@Cr ₂ O ₃ prepared in Example 1 of the present invention and CoCN prepared in Comparative Example 3;

Fig. 9 is the Raman spectrum of CoCN@Cr ₂ O ₃ prepared in Example 1 of the present invention and CoCN prepared in Comparative Example 3;

Figure 10 is the ORR polarization diagram of CoCN@Cr ₂ O ₃ prepared in Example 1 of the present invention, Pt/C in Comparative Example 1, CoCN prepared in Comparative Example 3, and Cr ₂ O ₃ prepared in Comparative Example 4 ( fuel cell field);

Fig. 11 is a test diagram of the catalytic efficiency of CoCN@Cr ₂ O ₃ prepared in Example 1 of the present invention and CoCN prepared in Comparative Example 3, including the number of electron transfers and the yield of by-product H ₂ O ₂ (fuel cell field);

Figure 12 is the half-cell it stability test chart of CoCN@Cr ₂ O ₃ prepared in Example 1 of the present invention, Pt/C in Comparative Example 1, and CoCN prepared in Comparative Example 3 for 10 hours (fuel cell and zinc- Air battery field);

Fig. 13 is an it stability test diagram of CoCN@Cr ₂ O ₃ half-cells prepared in Example 1 of the present invention for 50 hours continuously (in the field of fuel cells and zinc-air batteries);

Fig. 14 is a 10,000-cycle aging test diagram of CoCN@Cr ₂ O ₃ half-cells prepared in Example 1 of the present invention (in the field of fuel cells and zinc-air batteries);

Figure 15 is the long-term charge-discharge cycle performance diagram of CoCN@Cr ₂ O ₃ prepared in Example 1 of the present invention and the mixture of Comparative Examples 1 and 2 applied to ZABs (zinc-air battery field);

Figure 16 is the ORR polarization diagram of FeCN@Cr ₂ O ₃ prepared in Example 2 of the present invention and Pt/C in Comparative Example 1 (fuel cell field);

Figure 17 is the OER polarization diagram of NiCN@CrN prepared in Example 3 of the present invention and Ir/C in Comparative Example 2 (in the field of electrolyzed water);

Fig. 18 is a test diagram of the NiCN@CrN electrocatalytic OER stability test prepared in Example 3 of the present invention (in the field of electrolysis of water).

Detailed ways

The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should cover In the protection scope of the present invention.

In the present invention, a metal M-bipyridine solution is configured at room temperature, and stirred at room temperature so that M ions and bipyridine are fully coordinated and grown; then sodium chloride solid, chromium salt solid and organic ammonium salt are respectively added to the above solution and stirred The solid is completely dissolved; the above solution is placed on a heating platform, and the moisture in the solution is removed by rotary evaporation to obtain a solid mixture, and then the collected solid mixture is dried in a vacuum oven to obtain a mixed powder; finally The mixed powder is annealed under a protective atmosphere, and the sodium chloride template is removed by washing with water, and then pickling-suction-filtration-drying procedures are performed to obtain a chromium-based inorganic substance coupled transition metal nitrogen-doped carbon superstable catalyst.

The catalyst designed in the present invention is an ultra-thin two-dimensional plate-like chromium-based inorganic substance composed of many interconnected nanocrystals as a carrier. The open structure on both sides of the sheet can also effectively improve the efficiency of the mass transfer process and simplify the transportation of reaction intermediates and products. There are a large number of pores between the crystals, which allow the electrolyte and ions to be transported through the flakes, which can also greatly improve the mass transfer capacity of the catalyst. In addition, the introduced chromium-based inorganic carrier can improve the degree of graphitization of MNC, enhance the conductivity of the catalyst, and induce the electron spin polarization in the carbon layer where the MNC is located, improve catalytic selectivity and Faraday efficiency, and reduce the by-products. Formation, effectively inhibiting the damage of active oxygen species to the active sites of the catalyst. Compared with traditional carbon materials, chromium-based inorganic material supports have higher thermodynamic stability and corrosion resistance, so that MNCs coupled with chromium-based inorganic materials not only have higher catalytic activities such as ORR and OER, but also have high current and long-term Ultra-high durability under time cycles. In addition, the present invention can introduce inorganic carriers into different types of MNC (M=Co, Fe, Cu, Ni, etc.) atomically dispersed catalysts through the green and easy sodium chloride molten salt template method, which is widely used in ORR, Many catalytic fields such as OER and carbon dioxide reduction (CO ₂ RR) and energy conversion devices further improve the practical value of the present invention.

Example 1:

This embodiment provides the preparation method of CoCN@Cr ₂ O ₃ catalyst, including the following steps:

1. Co-bipyridine solution preparation: Weigh 24mg CoCl ₂ 6H ₂ O and 48mg 2,2'-bipyridine and dissolve them in 20mL ultrapure water respectively. After complete dissolution, mix the two solutions to obtain an orange-yellow solution and Stir at room temperature for 24 hours to fully coordinate the growth of Co ions and bipyridine;

2. Preparation of Co-Cr-organic ammonium salt mixed precursor: Add 20g NaCl, 24mg CrCl ₂ and 72mg organic ammonium salt to the solution prepared in step 1 and stir to completely dissolve the solid. Then, the above solution was placed on a heating platform at 65°C, and the moisture in the solution was removed by rotary evaporation to obtain a solid mixture, and then the collected solid mixture was heated and dried in a vacuum oven to remove the remaining moisture;

3. Preparation of Cr ₂ O ₃ coupled Co-NC composite catalyst: The precursor obtained in step 2 was thoroughly ground in a mortar, and then put into a tube furnace for calcination under an inert atmosphere. The protective atmosphere used is Ar or N ₂ inert gas, the carbonization temperature is 700°C, the carbonization time is 2h, and the heating rate is 2°C/min. Subsequently, the calcined product was dispersed into an aqueous solution, and the sodium chloride template was removed through multiple water washes. In order to remove the possible Co clusters, the template-removed product was dispersed into 0.5 mol L ^-1 dilute H ₂ SO ₄ aqueous solution, and kept stirring at 80°C for 5 h, after washing with water-suction filtration-vacuum The final flake Cr ₂ O ₃ coupled Co-NC composite ultrastable catalyst (CoCN@Cr ₂ O ₃ ) was obtained by drying;

The process flow of this embodiment is shown in FIG. 1 . The SEM, TEM, and HRTEM morphologies of CoCN@Cr ₂ O ₃ prepared under this process are shown in Figure 2, Figure 5, and Figure 6, respectively. The ICP test shows that the Co content is 1.02wt.%. The XPS spectrum of Co 2p and N1s in Cr ₂ O ₃ shows that Co in the catalyst exists as single-atom Co-N _x . Figure 9 shows the Raman spectrum before and after the introduction of inorganic supports. The introduction of Cr ₂ O ₃ improves the CoCN degree of graphitization. The ORR polarization test and catalytic efficiency test of the CoCN@Cr ₂ O ₃ catalyst are shown in Figure 10 and Figure 11, respectively. The electron transfer technique and the yield of by-product H ₂ O ₂ show that the catalytic efficiency is significantly improved after the introduction of Cr ₂ O ₃ , The stability test of the catalyst in RDE is shown in Figure 12, Figure 13, and Figure 14. The chromium salt inorganic substance greatly improves the stability of the catalyst so that the current retention rate is 100% in the 10-hour it test. It greatly exceeds that of noble metals and MNC catalysts, and the long-term cycle stability performance in ZABs batteries is shown in Figure 15, which can provide continuous and stable charge and discharge cycles for more than 1500 hours.

Example 2:

This embodiment provides the preparation method of FeCN@Cr ₂ O ₃ catalyst, including the following steps:

1. Preparation of Fe-bipyridine solution: Weigh 28mg FeCl ₃ 6H ₂ O and 48mg 2,2'-bipyridine and dissolve them in 20mL ultrapure water respectively. After complete dissolution, mix the two solutions to obtain an orange-yellow solution and Stir at room temperature for 24 hours to fully coordinate the growth of iron ions and bipyridine;

2. Preparation of Fe-Cr-organic ammonium salt mixed precursor: Add 20g NaCl, 24mg CrCl ₂ and 72mg urea to the solution prepared in step 1 and stir to completely dissolve the solid. Then, the above solution was placed on a heating platform at 65°C, and the moisture in the solution was removed by rotary evaporation to obtain a solid mixture, and then the collected solid mixture was heated and dried in a vacuum oven to remove the remaining moisture;

3. Preparation of Cr ₂ O ₃ coupled Fe-NC composite catalyst: The precursor obtained in step 2 was thoroughly ground in a mortar, and then put into a tube furnace for calcination under an inert atmosphere. The protective atmosphere used was Ar inert gas, the carbonization temperature was 700°C, the carbonization time was 2h, and the heating rate was 2°C/min. Subsequently, the calcined product was dispersed into an aqueous solution, and the sodium chloride template was removed through multiple water washes. In order to remove the possible Fe clusters, the template-removed product was dispersed into 0.5 mol L ^-1 dilute H ₂ SO ₄ aqueous solution, and kept stirring at 80°C for 5 h, after water washing-suction filtration-vacuum The final flaky Cr ₂ O ₃ coupled Fe-NC composite ultrastable catalyst (FeCN@Cr ₂ O ₃ ) was obtained by drying;

The process flow of this embodiment is shown in FIG. 1 . The SEM morphology of FeCN@Cr ₂ O ₃ prepared under this process is shown in Figure 3. The Fe content of ICP test is 1.52wt.%. The ORR polarization test of FeCN@Cr ₂ O ₃ catalyst is shown in Figure 16. The catalytic performance Obviously higher than the noble metal catalyst of Comparative Example 1, which represents that it has broad practical prospects in the field of fuel cells.

Example 3:

The present embodiment provides the preparation method of NiCN@CrN catalyst, comprises the following steps:

1. Preparation of Ni-bipyridine solution: Weigh 25mg NiCl ₂ 6H ₂ O and 48mg 2,2'-bipyridine and dissolve them in 20mL ultrapure water respectively. After complete dissolution, mix the two solutions to obtain an orange-yellow solution and Stir at room temperature for 24 hours to fully coordinate the growth of Co ions and bipyridine;

2. Preparation of Co-Cr-organic ammonium salt mixed precursor: Add 20g NaCl, 24mg CrCl ₂ and 72mg melamine to the solution prepared in step 1 and stir to completely dissolve the solid. Then, the above solution was placed on a heating platform at 65°C, and the moisture in the solution was removed by rotary evaporation to obtain a solid mixture, and then the collected solid mixture was heated and dried in a vacuum oven to remove the remaining moisture;

3. Preparation of CrN-coupled Ni-NC composite catalyst: Put the precursor obtained in step 2 into a mortar and thoroughly grind it, and then put it into a tube furnace for calcination under an inert atmosphere. The protective atmosphere used was Ar inert gas, the carbonization temperature was 650°C, the carbonization time was 2h, and the heating rate was 5°C/min. Subsequently, the calcined product was dispersed into an aqueous solution, and the sodium chloride template was removed through multiple water washes. In order to remove possible Ni clusters, the template-removed product was dispersed into 0.5 mol L ^-1 dilute H ₂ SO ₄ aqueous solution, and kept stirring at 80°C for 5 h, after washing with water-suction filtration-vacuum The final sheet-like CrN coupled Ni-NC composite ultrastable catalyst (NiCN@CrN) was obtained by drying;

The process flow of this embodiment is shown in FIG. 1 . The SEM morphology of NiCN@CrN prepared under this process is shown in Figure 4, and the Ni content measured by ICP is 1.34wt.%. The OER polarization test of the NiCN@CrN catalyst is shown in Figure 17, and the catalytic performance far exceeds that of the noble metal Comparative Example 2. In addition, the stability test of the catalyst in RDE is shown in Figure 18. After 10,000 cycles of aging, the catalytic performance is still excellent, which means that it has broad practical prospects in the field of fuel cells.

Comparative Example 1:

Purchase the latest commercial 20% Pt/C (Comm.20% Pt/C) from a certain company, and use it directly for testing without any treatment.

The ORR polarization test of Comm.20%Pt/C in this embodiment is shown in FIG. 7 . The RDE stability test is shown in Figure 10, and the catalytic stability is far less than that of CoCN@Cr ₂ O ₃ .

Comparative example 2:

Purchase the latest commercial Ir/C (Comm. 20% Ir/C) from a certain company, and use it directly for testing without any treatment.

The OER polarization test of Comm.20%Ir/C in this embodiment is shown in FIG. 17 .

Comparative example 3:

The CoCN that is not introduced into the inorganic carrier prepared by the sodium chloride molten salt template method is as follows:

1. Co-bipyridine solution preparation: Weigh 24mg CoCl ₂ 6H ₂ O and 48mg 2,2'-bipyridine and dissolve them in 20mL ultrapure water respectively. After complete dissolution, mix the two solutions to obtain an orange-yellow solution and Stir at room temperature for 24 hours to fully coordinate the growth of Co ions and bipyridine;

2. Preparation of Co-organic ammonium salt mixed precursor: Add 20 g of NaCl and 75 mg of urea to the solution prepared in step 1 and stir to completely dissolve the solid. Then, the above solution was placed on a heating platform at 65°C, and the moisture in the solution was removed by rotary evaporation to obtain a solid mixture, and then the collected solid mixture was heated and dried in a vacuum oven to remove the remaining moisture;

3. Preparation of CoCN catalyst without Cr ₂ O ₃ coupling: the precursor obtained in step 2 was thoroughly ground in a mortar, and then put into a tube furnace for calcination under an inert atmosphere. The protective atmosphere used is Ar or N ₂ inert gas, the carbonization temperature is 700°C, the carbonization time is 2h, and the heating rate is 2°C/min. Subsequently, the calcined product was dispersed into an aqueous solution, and the sodium chloride template was removed through multiple water washes. In order to remove the possible Co clusters, the template-removed product was dispersed into 0.5 mol L ^-1 dilute H ₂ SO ₄ aqueous solution, and kept stirring at 80°C for 5 h, after washing with water-suction filtration-vacuum The final flaky _{Cr2O3 -} free CoCN was obtained by drying;

The elemental valence state analysis (XPS test) and graphitization degree (Raman test) of CoCN prepared in this example are shown in Figure 7, Figure 8 and Figure 9 respectively; ORR polarization test, electron transfer number and _H of CoCN O ₂ yield test and RDE stability test are shown in Figure 10, Figure 11, and Figure 12, respectively. The ORR catalytic performance and electron transfer of CoCN are significantly lower than those of CoCN@Cr ₂ O ₃ in Example 1, and the by-product H ₂ O ₂ yield is higher, which proves that its catalytic efficiency is low and its catalytic stability is far inferior to that of CoCN. @Cr ₂ O ₃ .

Comparative example 4:

The _Cr2O3 carrier prepared by sodium chloride molten salt template method, the steps are as follows _:

1. Preparation of Cr-organic ammonium salt mixed precursor: Add 20g NaCl, 24mgCrCl ₂ and 72mg urea to 40ml ultrapure water and stir to completely dissolve the solid. Then, the above solution was placed on a heating platform at 65°C, and the moisture in the solution was removed by rotary evaporation to obtain a solid mixture, and then the collected solid mixture was heated and dried in a vacuum oven to remove the remaining moisture;

2. Preparation of Cr ₂ O ₃ inorganic matter: Put the precursor obtained in step 2 into a mortar and thoroughly grind it, and then put it into a tube furnace for calcination under an inert atmosphere. The protective atmosphere used is Ar or N ₂ inert gas, the carbonization temperature is 700°C, the carbonization time is 2h, and the heating rate is 2°C/min. Subsequently, the calcined product was dispersed into an aqueous solution, and the sodium chloride template was removed through multiple water washes, and the final flaky Cr ₂ O ₃ was obtained through suction filtration-vacuum drying.

The ORR polarization tests of the Cr ₂ O ₃ prepared in this example are shown in FIG. 7 . The ORR catalytic performance of Cr ₂ O ₃ is inferior to that of CoCN@Cr ₂ O ₃ .

Claims (8)

1. A preparation method of a chromium-based inorganic substance coupled transition metal nitrogen-doped carbon catalyst is characterized by comprising the following steps: the method comprises the following steps:

the method comprises the following steps: preparing a metal M-bipyridine solution:

weighing metal M salt and bipyridine, respectively dissolving the metal M salt and the bipyridine into ultrapure water at room temperature, mixing the two solutions after the metal M salt and the bipyridine are completely dissolved to obtain an orange yellow solution, and stirring at room temperature to ensure that M ions and the bipyridine are fully coordinated and grow;

step two: preparing an M-Cr-organic ammonium salt mixed precursor:

sequentially adding sodium chloride, chromium salt and organic ammonium salt into the orange solution obtained in the step one, and stirring to completely dissolve the solid; placing the solution on a heating platform, removing water in the solution by a rotary evaporation method to obtain a solid mixture, and placing the solid mixture in a vacuum oven for vacuum heating and drying to remove residual water to obtain an M-Cr-organic ammonium salt mixed precursor;

step three: preparing a chromium-based inorganic substance coupled M-N-C composite catalyst:

putting the precursor obtained in the step two into a mortar for full grinding, and then putting the precursor into a tube furnace for calcination treatment under the protective atmosphere; dispersing the calcined product into an aqueous solution, and removing a sodium chloride template through multiple times of water washing; dispersing the template-removed product into dilute H ₂ SO ₄ And (3) continuously stirring the mixture for 5 hours at the temperature of 80 ℃ in the aqueous solution, and carrying out water washing, suction filtration and vacuum drying to obtain the chromium-based inorganic substance coupled transition metal nitrogen-doped carbon catalyst.

2. The method for preparing the chromium-based inorganic substance coupled transition metal nitrogen-doped carbon catalyst according to claim 1, wherein the method comprises the following steps: in the first step, the molar ratio of the metal M salt to the bipyridine is 1:1 to 4.

3. The method for preparing the chromium-based inorganic substance coupled transition metal nitrogen-doped carbon catalyst according to claim 1, wherein the method comprises the following steps: in the first step, the metal M salt is one or more of ferric nitrate, ferric chloride, ferric acetate, ferrous nitrate, ferrous chloride, ferrous acetate, cobalt nitrate, cobalt chloride, cobalt acetate, copper nitrate, copper chloride, copper acetate, nickel nitrate, nickel chloride and nickel acetate, and the bipyridine is 2,2 '-bipyridine or 4,4' -bipyridine.

4. The method for preparing the chromium-based inorganic substance coupled transition metal nitrogen-doped carbon catalyst according to claim 1, wherein the method comprises the following steps: in the second step, the input amount of the sodium chloride is determined according to the volume of the M-bipyridyl solution, each milliliter of the solution corresponds to 0.5g of the sodium chloride, and the molar ratio of the chromium salt to the metal M salt is 1-8: 1, the mass ratio of the organic ammonium salt to the chromium salt is 3:1.

5. the method for preparing the chromium-based inorganic substance coupled transition metal nitrogen-doped carbon catalyst according to claim 1, wherein the method comprises the following steps: in the second step, the chromium salt is one of chromium chloride, chromium sulfate and chromium nitrate, and the organic ammonium salt is one of urea, melamine, dicyandiamide and ammonium citrate.

6. The method for preparing the chromium-based inorganic substance coupled transition metal nitrogen-doped carbon catalyst according to claim 3, wherein the method comprises the following steps: in the third step, the protective atmosphere is Ar or N ₂ The calcination temperature is 650-800 ℃, the time is 1-3h, and the heating rate is 2-10 ℃/min.

7. A chromium-based inorgano-coupled transition metal nitrogen-doped carbon catalyst prepared by the method of any one of claims 1 to 6.

8. Use of a chromium-based inorganic coupled transition metal nitrogen-doped carbon catalyst prepared by the method of any one of claims 1 to 6 in fuel cells, metal-air battery cathode oxygen reduction reactions and electrolysis of water oxygen evolution reactions.

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