CN114784301B - Non-noble metal cathode catalyst material and preparation method and application thereof - Google Patents

Abstract

The present invention discloses a non-precious metal cathode catalyst material and a preparation method and application thereof. The method comprises preparing a zeolite imidazolate metal organic framework polymer; ball milling mixing; molecular self-assembly and two-step pyrolysis. Also disclosed is the application of the catalyst prepared by the above method in a fuel cell. The method of the present invention can prepare nitrogen-carbon materials doped with transition metals with single atomic distribution in batches.

Description

A non-precious metal cathode catalyst material and its preparation method and application

Technical Field

The present invention relates to a non-precious metal cathode catalyst material and a preparation method and application thereof, and in particular to a preparation method for batch preparing a transition metal-doped nitrogen-carbon material with single-atom distribution for fuel cells.

Background technique

In the context of carbon peak, the use of clean energy without carbon emissions is being called for by the world. Hydrogen energy has attracted much attention due to its zero emissions. Among them, proton exchange membrane fuel cells are portable devices that directly convert hydrogen energy into electrical energy without going through the Carnot cycle. Therefore, they show great application potential in many fields (transportation, aerospace and military equipment, etc.). However, the electrocatalysts used in the electrodes of proton exchange membrane fuel cells, which are widely used in business today, are mainly Pt/C materials. The extreme scarcity of Pt resources has hindered its commercial development. The development of electrocatalyst materials that do not contain precious metal Pt is one of its ultimate solutions.

Among them, transition metal-doped nitrogen-carbon materials have been confirmed by researchers to be a reliable electrocatalyst material, and their activity in oxygen reduction is particularly outstanding. In this regard, researchers have carried out a lot of research, especially single-atom dispersed transition metal-doped nitrogen-carbon materials. However, the current preparation methods for single-atom non-precious metal-doped nitrogen-carbon catalyst materials are usually very complicated and can only be prepared at the experimental level, with low actual production significance and economy. For this reason, it is of great significance to develop a simple and portable transition metal-doped nitrogen-carbon material that can be prepared in batches with single-atom distribution.

Summary of the invention

The present invention firstly provides a method for preparing a non-noble metal cathode catalyst material, which can prepare nitrogen-carbon materials doped with transition metals with single-atom distribution in batches.

A method for preparing a non-precious metal cathode catalyst material, comprising:

The transition metal salt, the nitrogen-containing organic matter and the zeolite imidazolate metal organic framework material ZIF are mixed and ball-milled to obtain a uniform transition metal-containing powder mixture M/ZIF;

The powder mixture M/ZIF containing transition metal is dispersed in a solvent, so that the transition metal ions, nitrogen-containing organic matter and zeolite imidazolate metal organic framework material ZIF are coordinated with each other; then the transition metal ions and nitrogen-containing organic matter that are not coordinated are removed; and the M-ZIF precursor containing transition metal single atoms uniformly distributed is obtained by drying;

The M-ZIF precursor containing uniformly distributed transition metal single atoms is calcined and pyrolyzed in two steps to obtain a nitrogen-carbon material doped with a single-atom distributed transition metal, that is, a non-precious metal cathode catalyst material.

The present invention has found that the transition metal doped ZIF-8 mixture prepared by the traditional liquid phase adsorption method mainly relies on physical adsorption, so the adsorption amount of the transition metal depends largely on the specific surface area of ZIF-8, resulting in that the ZIF-8 prepared at present must have a very small particle size, and the preparation of small-particle ZIF-8 requires a very dilute Zn(NO ₃ ) ₂ ·6H ₂ O methanol solution, which greatly increases the consumption of methanol and increases the technical difficulty of mass production. The transition metal doped ZIF-8 mixture in the present invention has low requirements on the particle size of ZIF-8, because the distribution mode of the transition metal in the material of the present invention includes not only simple physical adsorption distribution, but also more in the form of coordination with nitrogen-containing organic matter (o-phenanthroline) to form a chelate, and then evenly distributed or coordinated on the ZIF-8 framework structure during the process of molecular reassembly. In addition, since the average size of the microporous channels in the organic skeleton of ZIF-8 is The average particle size of typical o-phenanthroline iron chelate particles is Therefore, it is difficult for o-phenanthroline iron chelate molecules to enter the internal framework structure of ZIF-8, and most of them are only attached to the surface layer of the ZIF-8 framework material by adsorption. The ball milling introduced in the present invention can completely pulverize the ZIF-8 regular dodecahedral framework and generate a large number of defects. Therefore, a composite material rich in monodisperse transition metals in both the surface layer and the bulk phase can be obtained during the subsequent molecular self-assembly.

Furthermore, the zeolite imidazolate metal organic framework material ZIF can be selected from ZIF-8 and ZIF-67.

In the present invention, the zeolite imidazolate metal organic framework material ZIF can be prepared by conventional methods in the art.

In some examples, the preparation method of zeolite imidazolate metal-organic framework material ZIF includes: dissolving zinc salt in methanol solvent, adding imidazole monomer (such as 2-methylimidazole) after complete dissolution, continuing to stir until the solution is milky white, then standing for emulsification, and finally centrifuging, washing, and drying to obtain zeolite imidazolate metal-organic framework material ZIF-8.

Furthermore, the mass ratio of the ball to the material during ball milling is 100 to 10:1.

Furthermore, the rotation speed of the ball mill is 200 to 1000 rpm, and the ball milling time is 1 to 24 hours.

The study found that ball milling under the above conditions can completely pulverize the framework structure of ZIF-8 material.

Furthermore, the mass ratio of the transition metal salt, the nitrogen-containing organic matter and the zeolite imidazolate metal organic framework material ZIF is 1:(5-20):(20-100), for example 1:10:40.

Furthermore, the transition metal is one or more of Fe, Cu, Co, Ni and Mn. The transition metal salt can be selected from one or more of chlorides, nitrates, sulfates, acetates, citrates and acetylacetonate compounds of the above transition metals.

Furthermore, the nitrogen-containing organic matter is one or more of o-phenanthroline, acetamide, ethylamine, pyrrole, aniline, ethylenediamine, dopamine, dicyandiamide, urea, butyronitrile, and melamine, preferably o-phenanthroline.

As a preferred embodiment of the present invention, the transition metal salt is one or more of chloride, nitrate, sulfate, acetate, citrate, and acetylacetonate compounds of Fe, preferably acetate (iron (II) acetate); the nitrogen-containing organic matter is o-phenanthroline. Due to the o-phenanthroline iron chelate formed by the transition metal salt (Fe, Co, Ni and Mn) and o-phenanthroline, the original catalytic performance can be guaranteed when the particle size and output of the prepared non-precious metal cathode catalyst material are increased.

Furthermore, the solvent for dispersing the transition metal-containing powder mixture M/ZIF can be selected from an alcohol/water mixed solvent, wherein the volume ratio of alcohol/water is 10 to 1: 1. The alcohol can be methanol or ethanol.

Furthermore, the method for removing the uncoordinated transition metal ions and nitrogen-containing organic matter may be centrifugation and/or washing.

Furthermore, in the two-step calcination and pyrolysis, the temperature range of the first step calcination and pyrolysis is 200°C to 600°C; the temperature range of the second step calcination and pyrolysis is 900°C to 1100°C.

The inventors have found that the first step of calcination and pyrolysis treatment under low temperature conditions can remove bound water and some unstable organic monomers in the composite material, while enhancing the coordination strength of transition metal elements and nitrogen elements, thereby stabilizing the distribution of single atoms. Then, the second step of calcination and pyrolysis treatment is carried out under high temperature conditions to pyrolyze and carbonize the composite material, thereby preparing a highly stable transition metal-doped nitrogen-carbon material. In particular, due to the use of the above two-step calcination and pyrolysis treatment, the non-precious metal cathode catalyst material prepared can maintain better catalytic performance when the particle size is increased, thereby increasing the yield.

In some examples, the first calcination and pyrolysis step may take place for 1-10 h, such as 2 h.

In some examples, the second step calcination and pyrolysis may be performed for 1-10 h, such as 1 h.

In some examples, the first calcination and pyrolysis temperature is 400° C. and the time is 2 h; the second calcination and pyrolysis temperature is 1000° C. and the time is 1 h.

In some examples, the method for preparing the non-precious metal cathode catalyst material comprises:

(1) dissolving zinc nitrate in a methanol solvent, adding imidazole monomer after it is completely dissolved, and continuing to stir until the solution is milky white, then standing for emulsification, and finally centrifuging, washing, and drying to obtain a zeolite imidazole ester metal organic framework material ZIF-8;

(2) adding iron salt, nitrogen-containing organic matter and zeolite imidazolate metal organic framework material ZIF-8 into a ball mill according to a certain proportion, and ball milling to obtain a uniform transition metal-containing powder mixture M/ZIF;

(3) dispersing the M/ZIF mixture in an alcohol/water mixed solvent, stirring it thoroughly and then letting it stand to allow the iron ions, nitrogen-containing ligands and ZIF-8 in the powder to coordinate with each other, removing the uncoordinated iron ions and monomers by centrifugation and washing, and drying to obtain a uniformly dispersed single-atom M-ZIF precursor;

(4) Finally, the M-ZIF precursor is placed in a tubular furnace and calcined and pyrolyzed in two steps to obtain the final single-atom dispersed M-N-C catalyst material.

The present invention also includes a non-precious metal cathode catalyst material prepared by the above method. The non-precious metal catalyst material is a nitrogen-doped carbon material with uniformly distributed transition metal atoms, wherein the transition metal is one or more of Fe, Cu, Co, Ni and Mn; and the transition metal content in the non-precious metal cathode catalyst material is 1wt% to 10wt%.

The material of the invention has single-atom dispersed M-N-C catalytic active sites and high active site density; through molecular self-assembly, metal ions in transition metal salts, nitrogen-containing ligands and metal organic framework polymers are coordinated with each other to obtain a uniformly dispersed single-atom M-ZIF precursor; finally, a single-atom dispersed M-N-C catalyst material is obtained through two-step pyrolysis, and is applied to the cathode of a fuel cell to exhibit excellent electrochemical performance.

The present invention also includes the use of the above non-precious metal cathode catalyst material in the preparation of proton exchange membrane fuel cells (including hydrogen-oxygen fuel cells and hydrogen-air fuel cells).

Basic principle: The uniformly mixed transition metal salts, nitrogen-containing complexes and imidazole metal-organic framework material ZIF-8 coordinate with each other in a mixed solvent. Due to the imidazole framework, electrostatic effects and the steric effect of the complex, the transition metal elements are effectively anchored in the imidazole framework structure in the form of single atoms. In the subsequent two-step pyrolysis, a single-atom distributed transition metal-doped nitrogen-carbon catalyst material is prepared.

Beneficial effects: Compared with the prior art, the present invention achieves at least one of the following significant effects: 1) Single-atom dispersed transition metal-doped nitrogen-carbon catalyst materials are prepared by molecular self-assembly strategy; 2) Single-atom catalyst materials with high active site density, high catalytic activity and high stability are prepared by two-step pyrolysis; 3) The preparation method is simple and controllable, with high consistency, and easy to achieve mass production; 4) It exhibits ultra-high output power when applied in fuel cells.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1: SEM image of the ZIF-8 precursor material prepared in Example 1 of the present invention.

FIG2 : Infrared test curve (FTIR) of ZIF-8 and Fe/ZIF materials prepared in Example 1 of the present invention.

FIG3 : HAADF diagram of Fe/N/C catalyst material prepared in Example 1 of the present invention.

FIG4 is a polarization curve diagram of the Fe/N/C catalyst material prepared in Example 1 of the present invention and used in a hydrogen-oxygen fuel cell.

Figure 5: Polarization curve diagram of the Fe/N/C catalyst material prepared in Example 1 of the present invention for use in a hydrogen-air fuel cell.

Figure 6: SEM image of the ZIF-8 precursor material prepared in Example 2 of the present invention.

FIG. 7 is a comparison of linear sweep voltammetry (LSV) curves of Fe/N/C catalyst materials prepared in Example 1 and Example 2 of the present invention.

FIG8 is a comparison diagram of linear sweep voltammetry (LSV) curves of Fe/N/C catalyst materials prepared in Example 1 of the present invention and Comparative Example 1.

FIG9 : A comparison of linear sweep voltammetry (LSV) curves of Fe/N/C catalyst materials prepared in Example 1 of the present invention and Comparative Example 2.

FIG10 : A comparison of linear sweep voltammetry (LSV) curves of Fe/N/C catalyst materials prepared in Example 1 of the present invention and Comparative Example 3.

FIG. 11 : A comparison of linear sweep voltammetry (LSV) curves of Fe/N/C catalyst materials prepared in Example 2 of the present invention and Comparative Example 4.

Detailed ways

The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the art or the product instructions are used. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased through regular channels.

Example 1

This embodiment provides a non-precious metal cathode catalyst material, and the preparation method thereof is as follows:

(1) Dissolve 10 g of Zn(NO ₃ ) ₂ ·6H ₂ O in 1 L of methanol and stir thoroughly. After the mixture is completely dissolved, weigh 11 g of 2-methylimidazole and stir thoroughly for 1 h to obtain a milky white solution. Let the solution stand for 24 h, then centrifuge, wash, and dry to prepare ZIF-8 (powder).

The method of this embodiment can produce an average of 3 g/batch of ZIF-8 powder.

(2) 50 mg of iron (II) acetate, 500 mg of 1,10-phenanthroline, and 2000 mg of ZIF-8 were weighed in a ratio of 1:10:40 and added to a ball mill. 100 g of ball mill beads (mixed zirconium oxide beads with particle sizes of 1 mm, 2 mm, and 3 mm) were weighed. The ball mill speed was set to 240 rpm and the ball milling time was 8 h. After the ball milling was completed, the powder was taken out to obtain a mixture of iron-containing elements, nitrogen-containing complexes, and imidazole metal-organic frameworks, Fe/ZIF.

(3) The Fe/ZIF mixture was dissolved in a methanol/water (volume ratio of 5:1) mixed solvent, stirred thoroughly for 1 h, and then allowed to stand for 12 h. After the powder was completely coordinated and crystallized, it was centrifuged, washed, and dried to obtain Fe-ZIF.

(5) Fe-ZIF powder was weighed into a corundum crucible, which was placed in a tube furnace and calcined twice in a nitrogen atmosphere. The first calcination temperature was 400°C for 2 h, and the second calcination temperature was 1000°C for 1 h.

In this example, 0.9 g of non-precious metal cathode catalyst material was prepared.

FIG. 1 is a SEM image of the ZIF-8 precursor material prepared in Example 1.

Fig. 2 is the infrared test curve (FTIR) figure of ZIF-8, Fe/ZIF material prepared in the present embodiment 1, wherein its N-H bond of ZIF-8 after doping has obvious right shift, shows that a large amount of electron withdrawing groups are introduced on its framework.Only o-phenanthroline group is present in the preparation method of embodiment, therefore fully proved that there is the form of coordination between o-phenanthroline iron and ZIF-8.

FIG3 is a HAADF diagram of the Fe/N/C catalyst material prepared in Example 1. It can be seen from FIG3 that all Fe elements are distributed in the form of single atoms.

FIG. 4 is a polarization curve diagram of the Fe/N/C catalyst material prepared in Example 1 for use in a hydrogen-oxygen fuel cell.

FIG5 is a polarization curve diagram of the Fe/N/C catalyst material prepared in Example 1 for use in a hydrogen-air fuel cell.

Example 2

This embodiment provides a non-precious metal cathode catalyst material, and its preparation method is different from that of Example 1 only in that: in step (1), the amount of "Zn(NO ₃ ) ₂ ·6H ₂ O" and "2-methylimidazole" added is increased tenfold year-on-year, that is, 100 g of "Zn(NO ₃ ) ₂ ·6H ₂ O" and 110 g of "2-methylimidazole" are added.

In this example, 6 g of non-precious metal cathode catalyst material was prepared.

Figure 6 is a SEM image of the ZIF-8 precursor material prepared in Example 2. It can be clearly seen that the particle size of the ZIF-8 obtained after the precursor concentration is simultaneously increased has a significant increase.

Figure 7 is a comparison of the linear sweep voltammetry (LSV) curves of the Fe/N/C catalyst materials prepared in Example 1 and Example 2 of the present invention. It can be inferred from Figure 7 that, although the particle sizes of the two catalysts differ greatly, their oxygen reduction catalytic activities differ little.

It can be seen that the output of ZIF-8 prepared in Example 2 increased year-on-year. More importantly, the particle size of the prepared ZIF-8 particles was several dozen times larger than that in Example 1, but the performance difference was very small.

Comparative Example 1

The only difference from Example 1 is that the "1,10-phenanthroline" nitrogen-containing coordination monomer in step (2) is omitted.

FIG8 is a comparison of linear sweep voltammetry (LSV) curves of Fe/N/C catalyst materials prepared in Example 1 of the present invention and Comparative Example 1. It can be inferred from FIG8 that the Fe/N/C catalyst material prepared in Comparative Example 1 without adding 1,10-phenanthroline nitrogen-containing monomer has a much lower oxygen reduction catalytic activity than Example 1.

Comparative Example 2

The only difference from Example 1 is that the ball milling step (2) is omitted.

Figure 9 is a comparison of the linear sweep voltammetry (LSV) curves of the Fe/N/C catalyst materials prepared in Example 1 of the present invention and in Comparative Example 2. It can be inferred from Figure 9 that the Fe/N/C catalyst material prepared in Comparative Example 2 without ball milling has a lower oxygen reduction catalytic activity than that of Example 1 after ball milling.

Comparative Example 3

The only difference from Example 1 is that step (5) is calcined only once, at a temperature of 1000° C. and for 1 h.

Figure 10 is a comparison of the linear sweep voltammetry (LSV) curves of the Fe/N/C catalyst materials prepared in Example 1 of the present invention and Comparative Example 3. It can be inferred from Figure 10 that the Fe/N/C catalyst material prepared by the second calcination in Example 1 has a higher oxygen reduction catalytic activity than the Comparative Example 3 prepared by the first calcination.

Comparative Example 4

The only difference from Example 2 is that step (5) is calcined only once, at a temperature of 1000° C. and for 1 h.

Figure 11 is a comparison of the linear sweep voltammetry (LSV) curves of the Fe/N/C catalyst materials prepared in Example 2 of the present invention and Comparative Example 4. It can be inferred from Figure 11 that the Fe/N/C catalyst material prepared by the second calcination in Example 2 has a higher oxygen reduction catalytic activity than the Comparative Example 4 prepared by the first calcination.

Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, these modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims (13)

1. A method for preparing a non-precious metal cathode catalyst material, comprising: The transition metal salt, the nitrogen-containing organic matter and the zeolite imidazolate metal organic framework material ZIF are mixed and ball-milled to obtain a uniform transition metal-containing powder mixture M/ZIF; The powder mixture M/ZIF containing transition metal is dispersed in a solvent, so that the transition metal ions, nitrogen-containing organic matter and zeolite imidazolate metal organic framework material ZIF are coordinated with each other; then the transition metal ions and nitrogen-containing organic matter that are not coordinated are removed; and the M-ZIF precursor containing transition metal single atoms uniformly distributed is obtained by drying; The M-ZIF precursor containing uniformly distributed transition metal single atoms is calcined and pyrolyzed in two steps to obtain a nitrogen-carbon material doped with a single-atom distributed transition metal, i.e., a non-noble metal cathode catalyst material; In the two-step calcination and pyrolysis, the temperature range of the first step calcination and pyrolysis is 200°C to 600°C, and the calcination and pyrolysis time is 1-10h; the temperature range of the second step calcination and pyrolysis is 900°C to 1100°C, and the calcination and pyrolysis time is 1-10h. 2. The method for preparing a non-precious metal cathode catalyst material according to claim 1, wherein the zeolite imidazolate metal organic framework material ZIF can be selected from ZIF-8, ZIF-67; and/or, The preparation method of the zeolite imidazolate metal organic framework material ZIF comprises: dissolving zinc salt in a methanol solvent, adding imidazole monomer after complete dissolution, continuing to stir until the solution is milky white, then standing for emulsification, and finally centrifuging, washing, and drying to obtain the zeolite imidazolate metal organic framework material ZIF. 3. The method for preparing a non-precious metal cathode catalyst material according to claim 1 or 2, wherein the mass ratio of the ball material during ball milling is 100 to 10:1; and/or, The ball mill has a rotation speed of 200 to 1000 rpm and a ball milling time of 1 to 24 hours. 4. The method for preparing a non-precious metal cathode catalyst material according to claim 1 or 2, wherein the mass ratio of the transition metal salt, the nitrogen-containing organic matter and the zeolite imidazolate metal organic framework material ZIF is 1:(5-20):(20-100). 5. The method for preparing a non-precious metal cathode catalyst material according to claim 1 or 2, wherein the mass ratio of the transition metal salt, the nitrogen-containing organic matter and the zeolite imidazolate metal organic framework material ZIF is 1:10:40. 6. The method for preparing a non-precious metal cathode catalyst material according to claim 1 or 2, wherein the transition metal is one or more of Fe, Cu, Co, Ni and Mn; preferably, the transition metal salt is one or more of chlorides, nitrates, sulfates, acetates, citrates and acetylacetonate compounds of the transition metal; and/or, The nitrogen-containing organic matter is one or more of o-phenanthroline, acetamide, ethylamine, pyrrole, aniline, ethylenediamine, dopamine, dicyandiamide, urea, butyronitrile and melamine. 7. The method for preparing a non-precious metal cathode catalyst material according to claim 1 or 2, wherein the transition metal salt is one or more of Fe chloride, nitrate, sulfate, acetate, citrate, and acetylacetonate compounds; and the nitrogen-containing organic compound is o-phenanthroline. 8. The method for preparing a non-precious metal cathode catalyst material according to claim 1 or 2, wherein the temperature of the first calcination pyrolysis is 400°C and the time is 2 hours; the temperature of the second calcination pyrolysis is 1000°C and the time is 1 hour. 9. The method for preparing the non-precious metal cathode catalyst material according to claim 1 or 2, comprising: (1) dissolving zinc nitrate in a methanol solvent, adding imidazole monomer after it is completely dissolved, and continuing to stir until the solution is milky white, then standing for emulsification, and finally centrifuging, washing, and drying to obtain a zeolite imidazole ester metal organic framework material ZIF-8; (2) adding iron salt, nitrogen-containing organic matter and zeolite imidazolate metal organic framework material ZIF-8 into a ball mill according to a certain proportion, and ball milling to obtain a uniform transition metal-containing powder mixture M/ZIF; (3) dispersing the M/ZIF mixture in an alcohol/water mixed solvent, stirring it thoroughly and then letting it stand to allow the iron ions, nitrogen-containing ligands and ZIF-8 in the powder to coordinate with each other, removing the uncoordinated iron ions and monomers by centrifugation and washing, and drying to obtain a uniformly dispersed single-atom M-ZIF precursor; (4) Finally, the M-ZIF precursor is placed in a tubular furnace and calcined and pyrolyzed in two steps to obtain the final single-atom dispersed M-N-C catalyst material. 10. A non-precious metal cathode catalyst material prepared by the method according to any one of claims 1 to 8. 11. The non-precious metal cathode catalyst material according to claim 10, characterized in that the transition metal in the non-precious metal cathode catalyst material is one or more of Fe, Cu, Co, Ni and Mn; and the transition metal content is 1wt% to 10wt%. 12. Use of the non-precious metal cathode catalyst material according to claim 10 or 11 in the preparation of a proton exchange membrane fuel cell. 13. The use according to claim 12, characterized in that the proton exchange membrane fuel cell comprises a hydrogen-oxygen fuel cell or a hydrogen-air fuel cell.