CN114204055B

CN114204055B - Cathode catalyst for fuel cell and preparation method and application thereof

Info

Publication number: CN114204055B
Application number: CN202111506040.XA
Authority: CN
Inventors: 王英; 陈佩佩; 李潇龙; 徐勋高; 漆海龙
Original assignee: China Automotive Innovation Corp
Current assignee: China Automotive Innovation Corp
Priority date: 2021-12-10
Filing date: 2021-12-10
Publication date: 2024-04-26
Anticipated expiration: 2041-12-10
Also published as: CN114204055A

Abstract

The invention provides a cathode catalyst for a fuel cell, a preparation method and application thereof. The cathode catalyst for the fuel cell comprises a nitrogen-doped porous carbon substrate and active particles growing on the nitrogen-doped porous carbon substrate, wherein the active particles comprise a metallic cobalt core and cobalt oxide coated on the surface of the core. The invention provides a cobalt-nitrogen Co-doped porous carbon composite material C-Co-N taking cobalt oxide as a shell metal cobalt as a core, which is provided with N-doped carbon materials with a multi-level pore structure, co-N _x catalytic sites, and CoO@Co nano particles with a core-shell structure, so that the oxygen reduction catalytic performance of the catalyst is improved through synergistic effect.

Description

Cathode catalyst for fuel cell and preparation method and application thereof

Technical Field

The invention belongs to the technical field of fuel cell catalyst preparation, and relates to a cathode catalyst for a fuel cell, and a preparation method and application thereof.

Background

With the rapid development of industrial society, the living standard of people is increasingly improved, and the following environmental problems are also more serious. Only one earth exists, and the environmental pollution cannot be ignored. The hydrogen fuel cell is used as a clean energy converter, the raw materials are hydrogen and air, the product is water, and no substances polluting the environment are produced, so that the hydrogen fuel cell is an ideal clean energy source. Wherein the cathode catalyst material is a main constraint factor in the popularization of hydrogen fuel cells.

The fuel cell cathode catalyst can be broadly classified into a noble metal catalyst, a non-noble metal catalyst, and a non-metal catalyst. Noble metals Pt and Pt-based alloys are currently considered to be the most widely used fuel cell catalysts with the best catalytic performance. However, the price of Pt resources is high, which leads to high production cost and scarcity of Pt resources, so that the commercial production on a large scale is limited. And in the fuel cell system, a catalyst poisoning phenomenon is liable to occur, and Pt also aggravates oxidation and corrosion phenomena of the carbon support during an Oxygen Reduction Reaction (ORR) until structural collapse is caused, thereby causing deactivation of the catalyst, thereby reducing the life of the electrode. Therefore, the development of the non-noble metal catalyst has great practical significance.

Non-noble metal catalysts are generally classified into the following: transition metals (mainly Fe, co, ni, etc.) and their oxides, sulfides and macrocyclic compounds. Nonmetallic catalysts are typically N, S, P, B and like heteroatom doped carbon materials. In particular, N-doped carbon materials, because N atoms are more electronegative than C atoms, resulting in uneven charge distribution in the carbon matrix, adjacent carbon atoms will become active sites for oxygen adsorption and reduction, thereby increasing the catalytic activity of ORR.

The porous carbon material has unique properties of high surface area, high porosity, high stability, high mechanical strength, higher conductivity and the like, and is an excellent carrier material.

CN102451727a discloses an M/N-C catalyst and its preparation and application, which uses cobalt salt and polypyrrole (PPy) to directly impregnate, so that Co and N on PPy act to form a catalytic center, and then directly heat-treating the sample to thermally decompose PPy to form a carbon skeleton, which is directly used as a carbon carrier of the novel catalyst to enhance the conductivity of the catalyst. Although polypyrrole can provide catalytic particles Fe, co and Ni with larger specific surface area after carbonization, the preparation process of the method is complex, has a plurality of influencing factors, needs high-temperature treatment in the polypyrrole carbonization process, needs inert gas protection to prevent the catalytic particles from oxidation, and the catalyst activity cannot meet the actual application requirements of the fuel cell.

CN102916203a discloses a cathode non-platinum catalyst of a proton exchange membrane fuel cell and a preparation method thereof, comprising the steps of preparing melamine formaldehyde resin, then adding metal salt, carrying out complexation reaction between the melamine formaldehyde resin and the metal salt to form a complex, evaporating a solvent, and then carrying out heat treatment decomposition to obtain the cathode non-platinum catalyst of the proton exchange membrane fuel cell with a hollow sphere structure. However, the melamine formaldehyde resin has poor conductivity, so that the conductivity of the catalyst is reduced, and similar to the scheme, the preparation of the hollow sphere structure cannot avoid the high-temperature heat treatment of organic matters, and the generation of complex component harmful gas generated in the hollow sphere structure is unfavorable for meeting the requirements of energy conservation and environmental protection.

Therefore, how to use cheap and easily available raw materials and obtain a fuel cell cathode oxygen reduction reaction catalyst with excellent catalytic activity by using a simple and easy-to-operate preparation method is a technical problem to be solved urgently.

Disclosure of Invention

The invention aims to provide a cathode catalyst for a fuel cell, a preparation method and application thereof. The invention provides a cobalt-nitrogen Co-doped porous carbon composite material C-Co-N taking cobalt oxide as a shell metal cobalt as a core, which is an N-doped carbon material with a multi-level pore structure to form a Co-N _x catalytic site, and meanwhile, the cobalt-nitrogen Co-doped porous carbon composite material C-Co-N is synergistic with CoO@Co nano particles with a core-shell structure to improve the oxygen reduction catalytic performance of a catalyst.

In order to achieve the aim of the invention, the invention adopts the following technical scheme:

In a first aspect, the present invention provides a cathode catalyst for a fuel cell, the cathode catalyst for a fuel cell comprising a nitrogen-doped porous carbon substrate and active particles grown on the nitrogen-doped porous carbon substrate, the active particles comprising a metallic cobalt core and cobalt oxide coated on the surface of the core.

The invention provides a cobalt-nitrogen Co-doped porous carbon composite material C-Co-N taking cobalt oxide as a shell metal cobalt as a core, which is an N-doped carbon material with a multi-level pore structure to form a Co-N _x catalytic site, and meanwhile, the cobalt-nitrogen Co-doped porous carbon composite material C-Co-N and the CoO@Co nano particles with a core-shell structure improve the oxygen reduction catalytic performance of a catalyst through synergistic effect.

In the invention, the porous carbon substrate is doped with N, and because the electronegativity of N atoms is stronger than that of C atoms, the charge distribution in the carbon substrate is uneven, and adjacent carbon atoms become active sites for oxygen adsorption and reduction, so that the catalytic activity of ORR is improved. If nitrogen doping is not performed, the catalytic activity of the catalyst on the ORR is affected.

Preferably, the feedstock for the cathode catalyst for a fuel cell comprises carbonaceous biomass, cobalt salt, and a nitrogen source.

In the invention, the carbonaceous biomass is selected as the raw material, the distribution is wide, the cost is low and the biomass is easy to obtain, and the biomass waste is preferably selected, so that waste materials are changed into valuable materials, various biological waste materials can be well treated, the carbon resources in the nature are fully utilized, the production cost of the carbon material is reduced, and the sustainable development is promoted.

Preferably, the nitrogen-doped porous carbon substrate further comprises elemental silicon.

In the invention, aiming at different types of carbonaceous biomasses, the catalyst also comprises silicon element, and the silicon element is also beneficial to the establishment of the active sites of the oxygen reduction catalyst.

Preferably, the mass ratio of the C element is 80 to 85%, for example 80%, 81%, 82%, 83%, 84%, 85%, or the like, based on 100% by mass of the cathode catalyst for a fuel cell.

Preferably, the mass ratio of the O element is 6 to 15%, for example, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, based on 100% by mass of the cathode catalyst for a fuel cell.

Preferably, the mass ratio of the N element is 3 to 6%, for example, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or the like, based on 100% by mass of the cathode catalyst for a fuel cell.

Preferably, the mass ratio of Si element is 1 to 4%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or the like, based on 100% by mass of the cathode catalyst for a fuel cell.

Preferably, the mass ratio of the Co element is 1 to 3%, for example, 1%, 1.5%, 2%, 2.5%, 3%, or the like, based on 100% by mass of the cathode catalyst for a fuel cell.

In the invention, the mass ratio of each element in the catalyst is synergistic, so that excellent oxygen reduction catalytic activity is realized together.

In a second aspect, the present invention provides a method for producing a cathode catalyst for a fuel cell according to the first aspect, the method comprising the steps of:

(1) Mixing carbonaceous biomass, cobalt salt and a regulator to obtain an alkaline mixed solution, carrying out hydrothermal treatment, and freeze-drying to obtain a precursor;

(2) And (3) carbonizing and heat-treating the precursor in the step (1) in a protective atmosphere to obtain the cathode catalyst for the fuel cell.

According to the invention, the carbon-containing biomass with wide sources is used as a raw material to prepare the oxygen reduction catalyst with excellent catalytic performance, the biomass material rich in carbon is subjected to hydrothermal treatment by cobalt salt, and then the porous carbon substrate doped with nitrogen and active particles growing on the porous carbon substrate doped with nitrogen are obtained through carbonization process, wherein the active particles comprise a metallic cobalt inner core and cobalt oxide coated on the surface of the inner core.

According to the invention, through the hydrothermal treatment of cobalt salt and biomass materials in a weakly alkaline solution, due to the action of oxygen-containing functional groups in the biomass and the subsequent nitrogen doping and carbonization process (nitrogen doping is not needed when the carbon-containing biomass contains nitrogen elements), the obtained active particles take the form of inner cores as metallic cobalt, outer layers are coated with cobalt oxide, and the hydrothermal synergistic effect with the subsequent nitrogen doping is realized, so that the cobalt nitrogen catalytic active sites are presented, the synergistic effect of the nitrogen doped porous carbon materials, co-Nx catalytic sites and CoO@Co nano particles with a core-shell structure is realized, and the excellent oxygen reduction catalytic performance of the catalyst material is achieved.

In the invention, the carbonaceous biomass is selected as the raw material, the distribution is wide, the method is low in cost and easy to obtain, biomass waste is preferred, waste materials are changed into valuable materials, various biological waste materials can be well treated, the carbon resources in the nature are fully utilized, the production cost of the carbon material is reduced, the sustainable development is promoted, and the carbonaceous biomass contains oxygen-containing functional groups, so that the CoO@Co core-shell structure can be favorably generated.

In the present invention, the mixed solution in the step (1) is weakly alkaline, so that the formation of Co-containing nanoparticles can be more easily achieved, and if it is non-alkaline, the formation of Co-containing nanoparticles is difficult.

In the present invention, carbonaceous biomass includes, but is not limited to, triarrhena, typha pollen ear or phoenix tree seed or bean curd refuse, etc.

Preferably, the cobalt salt of step (1) comprises cobalt acetate.

Preferably, the regulator of step (1) comprises aqueous ammonia.

In the invention, ammonia water is selected as a regulator, which is more beneficial to the formation of Co-containing nano particles.

Preferably, the pH of the alkaline mixed solution of step (1) is 8 to 10, e.g. 8, 8.5, 9, 9.5 or 10, etc.

In the invention, too large pH value can cause too large porous structure of the porous carbon material, the multi-stage porous structure is destroyed, and too small pH value is unfavorable for the formation of Co-containing nano particles.

Preferably, the temperature of the hydrothermal reaction in step (1) is 180 to 200 ℃, for example 180 ℃, 185 ℃, 190 ℃, 195 ℃, 200 ℃, or the like.

Preferably, the hydrothermal reaction in step (1) is carried out for a period of time ranging from 10 to 14 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours or 14 hours, etc.

In the invention, the hydrothermal time is too short, which is unfavorable for the formation of Co particles, and too long, and excessive growth of Co particles can occur.

Preferably, the time of the freeze-drying in step (1) is at least 24 hours, such as 24 hours, 28 hours, 30 hours or 35 hours, etc.

Preferably, in step (2), a nitrogen source is added to mix with the precursor of step (1).

In the present invention, when the carbonaceous biomass does not contain nitrogen, nitrogen doping is required.

Preferably, the nitrogen source comprises melamine.

Preferably, the temperature of the carbonization heat treatment in step (2) is 700 to 900 ℃, for example 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, or the like.

Preferably, the carbonization heat treatment in step (2) is performed for a period of 2 to 3 hours, for example, 2 hours or 3 hours, etc.

Preferably, the substance subjected to the carbonization heat treatment in the step (2) is sequentially subjected to water washing and sedimentation.

As a preferred technical scheme, the preparation method comprises the following steps:

(1) Mixing carbonaceous biomass, cobalt salt and ammonia water to obtain an alkaline mixed solution with the pH value of 8-10, carrying out hydrothermal treatment at 180-200 ℃ for 10-14 h, and carrying out freeze drying for at least 24h to obtain a precursor;

(2) And (3) mixing the precursor in the step (1) with a nitrogen source in a protective atmosphere, performing carbonization heat treatment for 2-3 hours at 700-900 ℃, washing with water, and settling to obtain the cathode catalyst for the fuel cell.

In a third aspect, the present invention also provides a fuel cell comprising the cathode catalyst for a fuel cell according to the first aspect.

Compared with the prior art, the invention has the following beneficial effects:

The invention provides a cobalt-nitrogen Co-doped porous carbon composite material C-Co-N taking cobalt oxide as a shell metal cobalt as a core, which is an N-doped carbon material with a multi-level pore structure to form a Co-N _x catalytic site, and meanwhile, the cobalt-nitrogen Co-doped porous carbon composite material C-Co-N is synergistic with CoO@Co nano particles with a core-shell structure to improve the oxygen reduction catalytic performance of a catalyst. The half-wave potential of the cathode catalyst for the fuel cell provided by the invention can reach more than 0.801V, the time and the pH value of the hydrothermal reaction can be further regulated, and the half-wave potential of the cathode catalyst can reach more than 0.835V.

Drawings

Fig. 1 is an XRD pattern of the cathode catalyst for fuel cell provided in example 1.

Fig. 2 is an SEM image of the cathode catalyst for a fuel cell provided in example 1.

Fig. 3 is a TEM image of the cathode catalyst for a fuel cell provided in example 1.

Fig. 4 is an XPS diagram of the cathode catalyst for a fuel cell provided in example 1.

Fig. 5 is an XPS diagram of the cathode catalyst for a fuel cell provided in example 1.

Fig. 6 is an XPS diagram of the cathode catalyst for a fuel cell provided in example 1.

Fig. 7 is a graph showing the electrochemical performance of the cathode catalysts for fuel cells provided in example 1 and comparative example 4.

Detailed Description

The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.

Example 1

The embodiment provides a cathode catalyst for a fuel cell, which comprises a nitrogen-doped porous carbon substrate and active particles growing on the nitrogen-doped porous carbon substrate, wherein the active particles comprise a metallic cobalt core and cobalt oxide coated on the surface of the core.

The preparation method of the catalyst comprises the following steps:

(1) Washing typha flowers with deionized water, naturally airing, bursting, shearing, weighing 0.9g, putting into a beaker a, adding 30ml of deionized water into 0.1g of cobalt acetate to prepare a solution, putting into a beaker b, pouring the typha flowers sheared in the beaker a into the solution of the beaker b, fully stirring and soaking, then dripping 5ml of ammonia water to adjust the pH value to 9, stirring uniformly, pouring into a hydrothermal kettle with the capacity of 40ml, putting into an oven, heating to 180 ℃ for 12h, pouring out the mixture after cooling to room temperature, extruding out liquid, only preserving solids, and freeze-drying for 24h to obtain a precursor;

(2) Taking a clean crucible, adding 0.4g of melamine at the bottom, weighing 0.6g of freeze-dried precursor (black brown solid) at the upper part of the crucible, carbonizing and heat treating for 2 hours at 800 ℃ in a vacuum furnace by taking nitrogen as a protective gas, cooling to room temperature to obtain black fluffy solid, grinding into black powder, washing with deionized water, and settling to obtain the catalyst material with cobalt oxide grown on a nitrogen-doped porous carbon substrate as a shell and metal cobalt as a core.

Fig. 1 shows the XRD pattern of the cathode catalyst for fuel cell provided in example 1, and as can be seen from fig. 1, the prepared materials include amorphous carbon substrate, co and CoO.

Fig. 2 shows an SEM image of the cathode catalyst for a fuel cell provided in example 1, fig. 3 shows a TEM image of the cathode catalyst for a fuel cell provided in example 1, and it can be seen from fig. 2 that the prepared material is a hierarchical pore carbon material substrate, and the morphology of Co particles uniformly grown and distributed is shown from fig. 3 that the Co particles are coo@co nanoparticles having a core-shell structure.

Fig. 4, 5 and 6 show XPS diagrams of the cathode catalyst for fuel cells provided in example 1, and as can be seen from fig. 4, the prepared material mainly contains C, N, O, si, co elements, each having a ratio of C (84%), O (9%), N (3%), si (2%), co (2%). Five peaks corresponding to pyridine-N (398.3 eV), co-N (399.7 eV), pyrrole-N (401.2 eV), graphite-N (402.6 eV) and N oxide (404.7 eV) can be seen from the high resolution spectrum of N1s of FIG. 5. The presence of Co-N bonds indicates the combination of Co and N, thereby forming Co-Nx catalytic active sites, and improving the catalytic activity of the catalyst. pyridine-N can effectively improve the initial potential and the wettability of materials of the ORR catalyst, and graphite-N can greatly improve the limiting current density of the ORR catalyst. The peaks for Co and Co2+ in the zero-valent state can be seen from FIG. 6, illustrating the presence of metallic cobalt and cobalt oxide.

Example 2

The preparation method of the catalyst comprises the following steps:

(1) Adding 30ml of deionized water into 0.1g of cobalt acetate to prepare a solution, weighing 1g of bean curd residue, pouring the solution into a beaker for multiple times, fully stirring and soaking, then dripping 5ml of ammonia water to adjust the pH value to 10, stirring uniformly, quickly pouring the solution into a hydrothermal kettle with the capacity of 40ml, putting the kettle into a baking oven, heating the kettle to 200 ℃ for hydrothermal treatment for 10 hours, pouring out the mixture after cooling to room temperature, extruding out the liquid, only preserving solids, and freeze-drying for 30 hours to obtain a precursor;

(2) Taking a clean crucible, weighing 0.5g of freeze-dried black brown solid, placing the solid at the bottom of the crucible, then taking nitrogen as a protective gas, carbonizing and heat treating for 2 hours at 900 ℃ in a vacuum furnace, cooling to room temperature to obtain black fluffy solid, grinding the black fluffy solid into black powder, washing the black powder with deionized water, and settling to obtain the catalyst material with cobalt oxide growing on a nitrogen-doped porous carbon substrate as a shell and cobalt as a core. Since the biomass itself is rich in N, no further nitrogen doping treatment is required.

Example 3

The preparation method of the catalyst comprises the following steps:

(1) Washing triarrhena yedoensis with deionized water, shearing, naturally airing, weighing 0.9g, putting into a beaker a, adding 30ml of deionized water into 0.1g of cobalt acetate to prepare a solution, putting into a beaker b, pouring the triarrhena yedoensis sheared in the beaker a into the solution of the beaker b, fully stirring and soaking, then dripping 5ml of ammonia water to adjust the pH value to 8, stirring uniformly, rapidly pouring into a hydrothermal kettle with the capacity of 40ml, putting into an oven, heating to 180 ℃ for 12h, pouring out the mixture after cooling to room temperature, extruding out liquid, only preserving solids, and freeze-drying for 35h to obtain a precursor;

(2) Taking a clean crucible, adding 0.36g of melamine at the bottom, weighing 0.58g of freeze-dried black brown solid, placing the solid at the upper part of the crucible, carbonizing and heat treating the solid in a vacuum furnace at 800 ℃ for 2 hours by taking nitrogen as a protective gas, cooling the solid to room temperature to obtain black fluffy solid, grinding the black fluffy solid into black powder, cleaning the black powder with deionized water, and settling the black powder to obtain the catalyst material taking cobalt oxide grown on a nitrogen-doped porous carbon substrate as a shell and metal cobalt as a core.

Example 4

The preparation method of the catalyst comprises the following steps:

(1) Washing triarrhena yedoensis with deionized water, shearing, naturally airing, weighing 0.9g, putting into a beaker a, adding 30ml of deionized water into 0.2g of cobalt acetate to prepare a solution, putting into a beaker b, pouring the triarrhena yedoensis sheared in the beaker a into the solution of the beaker b, fully stirring and soaking, then dripping 5ml of ammonia water to adjust the pH value to 8, stirring uniformly, quickly pouring into a hydrothermal kettle with the capacity of 40ml, putting into an oven, heating to 180 ℃ for 12h, pouring out the mixture after cooling to room temperature, extruding out the liquid, only preserving solids, and freeze-drying for 24h;

(2) Taking a clean crucible, adding 0.36g of melamine at the bottom, weighing 0.58g of freeze-dried black brown solid, placing the solid at the upper part of the crucible, carbonizing and heat treating the solid in a vacuum furnace at 800 ℃ for 2 hours by taking nitrogen as a protective gas, cooling the solid to room temperature to obtain black fluffy solid, grinding the black fluffy solid into black powder, cleaning the black powder with deionized water, settling the black powder, and obtaining the catalyst material taking cobalt oxide grown on a nitrogen-doped porous carbon substrate as a shell and metallic cobalt as a core.

Example 5

The difference between this example and example 1 is that the hydrothermal time in step (1) of this example is 8h.

The remaining preparation methods and parameters were consistent with example 1.

Example 6

The difference between this example and example 1 is that the hydrothermal time in step (1) of this example is 15h.

Example 7

The difference between this example and example 1 is that the pH in step (1) of this example was 12.

Comparative example 1

The difference between this comparative example and example 1 is that no ammonia regulator was added in step (1) of this comparative example.

Comparative example 2

The difference between this comparative example and example 1 is that the conventional oven drying was used in step (1) of this comparative example, and freeze drying was not used.

Comparative example 3

The difference between this comparative example and example 1 is that melamine was not added in step (2) of this comparative example, and argon was used as a shielding gas.

Comparative example 4

This comparative example provides a cathode catalyst for a fuel cell, which is a commercial Pt/C catalyst.

Fig. 7 is an electrochemical performance graph of the cathode catalysts for fuel cells provided in example 1 and comparative example 4, and it can be seen from fig. 7 that the catalyst prepared by the method of example 1 has comparable catalytic oxygen reduction performance to the conventional Pt/C catalyst.

Table 1 shows the elemental components and the contents of the cathode catalysts for fuel cells provided in examples 1 to 7.

TABLE 1

	C(％)	O(％)	N(％)	Co(％)	Si(％)
						Example 1	84	9	3	2	2
Example 2	85	8	4	2	1
						Example 3	85	8	3	2	2
Example 4	83	9	3	3	2
						Example 5	83	10	4	1	2
Example 6	80	11	4	4	1
						Example 7	80	12	3	4	1

Electrochemical performance tests were conducted on the cathode catalysts for fuel cells provided in examples 1 to 7 and comparative examples 1 to 4 under the following test conditions:

1) Preparing KOH solution with the concentration of 0.1 mol.L ^-1, sealing and placing in a dark place, and introducing high-purity oxygen into the solution before electrochemical test;

2) The electrochemical workstation model is CHI760E (Shanghai Chenhua instruments Co., ltd.), in a three-electrode system, graphite is used as a counter electrode, a mercury/mercury oxide electrode (Hg/HgO) is used as a reference electrode, a core-shell structure doped porous carbon material is directly used as a working electrode, an ORR (non-noble metal redox) electrochemical performance of the porous carbon material is tested in 0.1mol.L ^-1 KOH electrolyte by adopting a Linear Scanning Voltammetry (LSV), and an ORR half-wave potential E1/2 (vs. RHE) is obtained after the test, and the result is shown in a table 2.

TABLE 2

	Half-wave potential (V)
		Example 1	0.847
Example 2	0.843
		Example 3	0.848
Example 4	0.835
		Example 5	0.803
Example 6	0.81
		Example 7	0.801
Comparative example 1	0.798
		Comparative example 2	0.786
Comparative example 3	0.769
		Comparative example 4	0.823

The catalyst performance can be judged by the half-wave potential in the table 1, and the larger the initial potential is, the larger the limiting current density is, and the larger the half-wave potential is, the better the catalyst performance is.

From the data of examples 1 and 5 and 6, it is clear that hydrothermal time is too short, which is unfavorable for the formation of Co particles at the catalytic site, and too long, and excessive growth of Co particles occurs. Both of these cases are disadvantageous for the improvement of the catalytic activity of the catalyst for oxygen reduction.

From the data of example 1 and example 7, it is apparent that an excessive pH value in step (1) results in an excessively large porous carbon material pore structure, a broken hierarchical pore structure, and a reduced specific surface area of the material.

From the data of example 1 and comparative example 1, it is clear that the addition of no ammonia modifier will result in too low a pH to favor the formation of active sites containing Co nanoparticles.

From the data of example 1 and comparative example 2, it is understood that the formation and maintenance of the hierarchical pore structure is not facilitated by the absence of lyophilization, and the exposure of the catalytic sites is not facilitated.

From the data of example 1 and comparative example 3, it is understood that formation of nitrogen-doped carbon active sites and formation of Co-N _x active sites cannot be achieved without nitrogen doping.

As can be seen from the data results of example 1 and comparative example 4, compared with the conventional Pt/C catalyst, the catalyst provided by the invention has the advantages of equivalent catalytic oxygen reduction performance, low cost and easy obtainment of raw materials, simple preparation method and low possibility of catalyst poisoning.

In summary, the invention provides the cobalt-nitrogen Co-doped porous carbon composite material C-Co-N which takes cobalt oxide as a shell metal cobalt as a core, has N-doped carbon materials with a multi-level pore structure, forms Co-N _x catalytic sites, and improves the oxygen reduction catalytic performance of the catalyst through synergistic effect with CoO@Co nano particles with a core-shell structure. The half-wave potential of the cathode catalyst for the fuel cell provided by the invention can reach more than 0.801V, the time and the pH value of the hydrothermal reaction can be further regulated, and the half-wave potential of the cathode catalyst can reach more than 0.835V.

The applicant declares that the above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present invention disclosed by the present invention fall within the scope of the present invention and the disclosure.

Claims

1. The preparation method of the cathode catalyst for the fuel cell is characterized in that the cathode catalyst for the fuel cell comprises a cobalt-nitrogen co-doped porous carbon substrate and active particles growing on the cobalt-nitrogen co-doped porous carbon substrate, wherein the active particles consist of a metal cobalt inner core and cobalt oxide coated on the surface of the inner core;

the preparation method of the cathode catalyst for the fuel cell comprises the following steps:

(1) Mixing carbonaceous biomass, cobalt salt and ammonia water to obtain an alkaline mixed solution, carrying out hydrothermal treatment, and freeze-drying to obtain a precursor; (2) Carbonizing the precursor in the step (1) in a protective atmosphere to obtain the cathode catalyst for the fuel cell;

the pH value of the alkaline mixed solution in the step (1) is 8-10;

the temperature of the hydrothermal reaction in the step (1) is 180-200 ℃;

The hydrothermal reaction time in the step (1) is 10-14 h.

2. The method for producing a cathode catalyst for a fuel cell according to claim 1, wherein the raw material of the cathode catalyst for a fuel cell further comprises a nitrogen source.

3. The method for producing a cathode catalyst for a fuel cell according to claim 1, wherein the cobalt-nitrogen co-doped porous carbon substrate further comprises elemental silicon.

4. The method for producing a cathode catalyst for a fuel cell according to claim 3, wherein the mass ratio of the element C is 80 to 85% based on 100% of the mass of the cathode catalyst for a fuel cell.

5. The method for producing a cathode catalyst for a fuel cell according to claim 3, wherein the mass ratio of the O element is 6 to 15% based on 100% of the mass of the cathode catalyst for a fuel cell.

6. The method for producing a cathode catalyst for a fuel cell according to claim 3, wherein the mass ratio of the element N is 3 to 6% based on 100% of the mass of the cathode catalyst for a fuel cell.

7. The method for producing a cathode catalyst for a fuel cell according to claim 3, wherein the mass ratio of Si element is 1 to 4% based on 100% of the mass of the cathode catalyst for a fuel cell.

8. The method for producing a cathode catalyst for a fuel cell according to claim 3, wherein the mass ratio of Co element is 1 to 3% based on 100% of the mass of the cathode catalyst for a fuel cell.

9. The method for producing a cathode catalyst for a fuel cell according to claim 1, wherein the cobalt salt in step (1) comprises cobalt acetate.

10. The method for producing a cathode catalyst for a fuel cell according to claim 1, wherein the time for freeze-drying in step (1) is at least 24 hours.

11. The method for producing a cathode catalyst for a fuel cell according to claim 1, wherein in the step (2), a nitrogen source is added and mixed with the precursor of the step (1).

12. The method for producing a cathode catalyst for a fuel cell according to claim 11, wherein the nitrogen source comprises melamine.

13. The method for producing a cathode catalyst for a fuel cell according to claim 1, wherein the carbonization heat treatment in step (2) is performed at a temperature of 700 to 900 ℃.

14. The method for producing a cathode catalyst for a fuel cell according to claim 1, wherein the carbonization heat treatment in step (2) is performed for 2 to 3 hours.

15. The method for producing a cathode catalyst for a fuel cell according to claim 1, wherein the carbonized material obtained in the step (2) is washed with water and then settled in this order.

16. The method for producing a cathode catalyst for a fuel cell according to claim 1, characterized in that the method comprises the steps of:

(1) Mixing carbon-containing biomass, cobalt salt and ammonia water to obtain an alkaline mixed solution with a pH value of 8-10, carrying out hydrothermal treatment at 180-200 ℃ for 10-14 h, and carrying out freeze drying for at least 24h to obtain a precursor;

17. A fuel cell comprising the cathode catalyst for a fuel cell prepared by the preparation method according to any one of claims 1 to 16.