CN103721748B - High-efficiency oxygen molecule reduction base metal catalyst and preparation thereof - Google Patents

Abstract

The invention provides a preparation method of a class of high-efficiency oxygen molecule reduction base metal catalyst. Specifically, the present invention provides a composite catalytic system having the following structure of formula I: wherein, the definition of each structural component is as described in the specification. The composite system of the present invention can be used to catalyze the reduction reaction of oxygen molecules. As an electrocatalyst for the reduction of oxygen molecules, it has excellent catalytic performance and can replace the existing precious metal platinum catalysts. It has great potential application prospects in the fields of fuel cell electric vehicles and the like. commercial value. Carrier‑(Linker‑Ligand‑Metal complex) _nFormula I.

Description

Efficient Oxygen Molecular Reduction Base Metal Catalyst and Its Preparation

technical field

The invention relates to the field of fuel cell catalysts, in particular, the invention provides a class of high-efficiency oxygen molecule reduction base metal catalysts and a preparation method thereof.

Background technique

A fuel cell is a device that directly converts the chemical energy of fuel (such as hydrogen) and oxygen into electrical energy through an electrode chemical reaction, and its anode is a hydrogen electrode (hydrogen is oxidized and decomposed into protons and electrons: H ₂ → 2H ⁺ +2e ^- ), the cathode is an oxygen electrode (oxygen is reduced to water: 1/2O ₂ +2H ⁺ +2e ^- →H ₂ O), and a certain amount of catalyst is loaded on the anode and cathode to accelerate the electrochemical reaction on the electrode. Fuel cells, especially proton exchange membrane fuel cells (Polymer Electrolyte Membrane Fuel Cells, PEMFC), have the characteristics of low operating temperature, short start-up time, high conversion efficiency, clean emission (product is water), etc., and have great potential in future transportation applications. potential. Although the research and development technology of fuel cells is very mature, a "bottleneck" that plagues the large-scale commercial production of fuel cell electric vehicles is that the cost of batteries is too high (mainly due to the high cost of its electrode electrocatalyst). Currently, fuel cell electrocatalysts are mainly platinum-group noble metals. Due to the high price of the rare metal platinum and the problem of continuous supply in the future, it is particularly important to develop new base metal electrocatalysts.

Non-platinum catalysts, that is, base metal catalysts, have always been the focus of research on electrocatalysts for the reduction of oxygen molecules. Cobalt, iron, manganese and other transition metal complexes, including their macrocyclic complexes, have been used as ORR catalysts, and some of them have good activity. These base metal catalysts finally need to be treated at high temperature (≥500 degrees Celsius) to show high catalytic activity and stability, but after high temperature heat treatment, the metal (macrocyclic) complex initially added has been decomposed, resulting in catalyst active center species unknown. In addition, the durability of the catalyst is poor. In recent years, the research on base metal catalysts has received further extensive attention and breakthroughs. The Zelenay research group in the United States obtained Co-PPY-C, a carbon-supported catalyst coordinated by pyrrole and cobalt, by adding cobalt acetate to polypyrrole (PPY)-wrapped carbon powder and then reducing it with NaBH ₄ . ORR catalytic activity, but the sustained stability is not high. The research group then further improved the preparation of the catalyst by first mixing aniline, carbon powder, cobalt and iron-containing salts, and then through oxidative polymerization → high temperature treatment under nitrogen and ammonia atmosphere → acid rinsing and other steps. Base metal electrocatalysts with high catalytic activity and durability nearly comparable to platinum catalysts. Recently, they prepared nitrogen-doped N-Fe-CNT/CNP composite catalysts by simply mixing and calcining carbon nanotubes, nitrogen-containing precursors, and metal iron salts. The composite catalyst exhibits ORR catalytic activity similar to that of commercial Pt/C under alkaline conditions. The Dodelet research group in Canada reported that nitrogen-containing ligands (such as o-phenanthroline) and iron acetate were added to the microporous structure of microcrystalline carbon by ball milling technology, and then obtained by high-temperature treatment under argon and ammonia atmospheres. Highly active ORR electrocatalysts, but the catalyst stability is still not high enough to compete with platinum catalysts. Recently, they encapsulated iron salt and nitrogen-containing precursors with MOFs framework structure, and then prepared a new ORR catalyst by high-temperature calcination, which exhibited high volume activity and mass transfer performance. In addition, metal-free (metal-free) nitrogen and fluorine-doped carbon material ORR catalysts have also been studied a lot. Such catalysts generally have better ORR catalytic performance in alkaline conditions, and rarely compare with platinum/carbon in acidic environments. The catalytic performance of the catalyst, the amount of nitrogen and fluorine doping in the carbon material and the doping process are often difficult to control.

In conclusion, with the increasing demand for new energy sources, the research on base metal ORR electrocatalysts has flourished in recent years. However, the preparation process of base metal ORR catalysts often requires high-temperature treatment. This heat treatment process completely destroys the structural characteristics of the initial complexes, and the reactivity of the catalyst cannot be adjusted by changing the structure and properties of the catalyst. In addition, most of the base metal ORR electrocatalysts reported so far only show high catalytic activity in alkaline environment, and only a few of them have comparable catalytic activity to Pt/C catalysts.

To sum up, there is an urgent need in this field to develop a low-cost, simple preparation method, easy-to-control reaction, and high catalytic activity under both alkaline and acidic conditions for the reduction of oxygen molecules.

Contents of the invention

The object of the present invention is to provide a catalyst for the reduction reaction of oxygen molecules which has a simple preparation method, is easy to control the reaction, and exhibits high catalytic activity under both alkaline and acidic conditions.

A first aspect of the present invention provides a composite catalyst with the following structure:

Carrier-(Linker-Ligand-Metal complex) _n formula I

in,

"-" represents a chemical bond, and the chemical bond is a covalent bond or a coordination bond;

Carrier is a carbon-based matrix carrier;

Ligand is a nitrogen-containing five-membered or six-membered heterocyclic coordination group;

Linker is a linking molecule, and the linking molecule is respectively connected to a carbon-based carrier and a nitrogen-containing five-membered or six-membered heterocyclic coordination group through a covalent bond;

Metal complex is selected from the following group: substituted or unsubstituted iron, cobalt, manganese porphyrin molecules; substituted or unsubstituted iron, cobalt, manganese phthalocyanine molecules; substituted or unsubstituted iron, cobalt, manganese corrin molecules; Copper, iron, cobalt, and manganese complexes coordinated by nitrogen ligands; the Metal complex forms a coordination bond with the nitrogen atom on the nitrogen-containing five-membered or six-membered heterocyclic ring;

n≥1.

In another preferred example, the carrier is selected from the group consisting of single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene; preferably, the carrier is multi-walled carbon nanotubes.

In another preferred example, the Ligand is selected from the group consisting of imidazolyl, pyridyl or polypyridyl.

In another preferred example, the Linker is selected from the group consisting of substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclic aromatic.

In another preferred example, the Linker is a substituted or unsubstituted heterocyclic aromatic group, wherein the heterocyclic aromatic group has 3-9 nitrogen atoms.

In another preferred example, there is at least one aromatic ring structural unit in the Linker.

In another preferred example, the Linker has the following structure:

In another preferred example, the Metal complex has an iron-based porphyrin with the following structure:

In the formula, Ar is selected from the group consisting of substituted or unsubstituted aryl groups, substituted or unsubstituted azacyclic aromatic groups.

In another preference, the Metal complex is iron porphyrin with the following structure:

Wherein, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , and R ₇ are each independently selected from the following group: H, halogen, substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C1-C4 alkyl-oxyl, carboxyl, amino, amido.

In another preferred example, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , and R ₇ are each independently selected from the following group: H, F, Cl, Br, CH ₃ , CF ₃ , carboxyl , COOCH ₃ .

In another preferred example, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ and R ₇ are all H.

In another preferred example, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , and R ₇ are all F.

In another preferred example, R ₁ , R ₃ , R ₄ , R ₆ and R ₇ are all CH ₃ , and R ₂ and R ₅ are all H.

In another preferred example, R ₁ , R ₄ , and R ₇ are all F, and R ₂ , R ₃ , R ₅ , and R ₆ are all H.

In another preferred example, R ₁ , R ₂ , R ₄ , R ₅ , and R ₇ are all H, and R ₃ and R ₆ are all CF ₃ .

In another preferred example, R ₁ , R ₂ , R ₃ , R ₅ , R ₆ , and R ₇ are all H, and R ₄ is COOH or COOCH ₃ .

In another preferred example, R ₁ , R ₂ , R ₃ , R ₅ and R ₆ are all H, and R ₄ and R ₇ are COOH or COOCH ₃ .

In another preferred example, R ₁ is F, R ₂ , R ₃ , R ₅ , R ₆ and R ₇ are all H, and R ₄ is COOH or COOCH ₃ .

In another preferred example, R ₁ is F, R ₂ , R ₃ , R ₅ and R ₆ are all H, and R ₄ and R ₇ are COOH or COOCH ₃ .

In another preferred example, R ₁ is F, R ₂ , R ₃ , R ₅ and R ₆ are all H, and R ₄ and R ₇ are COOH or COOCH ₃ .

In another preferred example, R ₁ , R ₂ , R ₃ , R ₅ , R ₆ , and R ₇ are all F, and R ₄ is COOH or COOCH ₃ .

In another preferred example, R ₁ , R ₂ , R ₃ , R ₅ , and R ₆ are all F, and R ₄ , R ₇ are COOH or COOCH ₃ .

In another preferred example, R ₁ , R ₂ , R ₅ , R ₆ , and R ₇ are all H, R ₃ is CF ₃ , and R ₄ is COOH or COOCH ₃ .

In another preferred example, R ₁ , R ₂ , R ₅ , and R ₆ are all H, R ₃ is CF ₃ , and R ₄ , R ₇ are COOH or COOCH ₃ .

A second aspect of the present invention provides a method for preparing a catalyst as described in the first aspect of the present invention, said method comprising the steps of:

(i) Provide a carbon-based carrier Carrier-(Linker-Ligand) _n as shown in formula Ia, the surface of which is modified with a linker molecule and a nitrogen-containing five-membered or six-membered heterocyclic coordination group, wherein the linker molecule The Linker is connected to the surface of the carbon-based carrier Carrier through a covalent chemical bond, and the nitrogen-containing five-membered or six-membered heterocyclic group Ligand is connected to the linker molecule Linker through a covalent chemical bond;

Carrier-(Linker-Ligand) _m type Ia

(ii) using a substituted or unsubstituted Metal complex to react with the Carrier-(Linker-Ligand) _m to form a compound shown in formula I;

Carrier-(Linker-Ligand-Metal complex) _n formula I

Wherein, the definitions of Carrier, Linker, Ligand, Metal complex, and n are as described in the first aspect of the present invention; m≥1, and m and n may be equal or unequal.

In another preferred example, in the preparation method, both steps (i) and (ii) are carried out at ≤80°C.

In another preferred example, m≥n.

In another preferred example, in the compound of formula I prepared in the step (ii), the surface of the carbon-based carrier carrier contains some -Linker-Ligand surface modification groups that are not coordinated with the Metal complex.

In another preferred embodiment, the compound of formula Ia is prepared by a method comprising the following steps:

Provide carbon-based carrier Carrier;

Using a coupling reagent to modify the surface of the carbon-based carrier Carrier to form a carbon-based carrier with a La modification on the surface;

In situ formation of said nitrogen-containing five-membered or six-membered heterocyclic group on the linker molecule yields a compound of formula Ia.

In another preferred embodiment, said La is the same as or different from Linker.

In another preferred embodiment, the compound of formula Ia is prepared by a method comprising the following steps:

(a) Provide carbon-based carrier Carrier;

(b) surface-modify the carbon-based carrier Carrier with one or more coupling reagents to obtain a surface-modified carbon-based carrier Carrier-(Linker-Ligand) _m ; wherein, in the coupling reagents, at least one The structure of the species contains a nitrogen-containing five-membered or six-membered heterocyclic group.

In another preferred embodiment, the compound of formula Ia is prepared by a method comprising the following steps:

(a) Provide carbon-based carrier Carrier;

(b) surface-modify the carbon-based carrier Carrier with a coupling reagent Linker'-X to obtain a surface-modified carbon-based carrier Carrier-(Linker') _m ;

(c) react the reagent Ligand-Linker'' containing nitrogen-containing five-membered or six-membered heterocyclic group in the structure with the surface-modified carbon-based carrier Carrier-(Linker') _m to obtain a surface-modified The carbon-based carrier Carrier-(Linker-Ligand) _m of the group;

Among them, Linker' and Linker'' are linking molecules including all or part of the structure of Linker, and Linker' and Linker'' can react to form Linker;

X is a leaving group.

In another preferred embodiment, the Linker' is phenyl.

In another preferred example, the Linker'-X is triisopropylsilynylphenylazofluoroborate.

In another preferred example, the step (b) is performed in the presence of a reducing agent, preferably, the reducing agent is hydrazine hydrate.

In another preferred example, the Linker" is 4-azidophenyl.

In another preference, the Ligand-Linker "is 1-(4-azidophenyl) imidazole.

The third aspect of the present invention provides the use of the catalyst according to the first aspect of the present invention as a catalyst for the reduction reaction of oxygen molecules.

In another preferred example, the oxygen molecule reduction reaction is carried out in an alkaline or acidic environment. Preferably, the acidic environment refers to the pH of the reaction system≤5; the alkaline environment refers to the pH of the reaction system≥13.

The fourth aspect of the present invention provides an oxygen molecule reduction catalyst, which includes the catalyst as described in the first aspect of the present invention.

A fifth aspect of the present invention provides a fuel cell, characterized in that the fuel cell includes the catalyst described in the first aspect of the present invention.

In another preferred example, the electrode catalyst of the fuel cell includes the catalyst described in the first aspect of the present invention

It should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described in the following (such as embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, we will not repeat them here.

Description of drawings

Fig. 1 ORR polarization curves of catalysts in alkaline environment. Black solid line: 20%Pt/C; Red solid line: CNTImFeF ₂ TPP (0.1M KOH,@1600rpm; CNTImFeF ₂ TPP: corresponding to the fourth compound in Table 1, that is, R ₁ =R ₄ =R ₇ =F, R ₂ =R ₃ =R ₅ =R ₆ =H).

Fig. 2 Curve of the percentage of H ₂ O ₂ generated on the disk working electrode in alkaline environment versus potential. Black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M KOH, @1600rpm).

Figure 3 Stability of catalysts in alkaline environments. Black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M KOH, @0.7V vs RHE, 900rpm).

Figure 4 ORR polarization curves of catalysts in acidic environment, black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M HClO ₄ ,@1600rpm).

Fig. 5 The percentage of H ₂ O ₂ generated on the disk working electrode in an acidic environment varies with potential. Black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M HClO ₄ ,@1600rpm).

Figure 6 Stability of catalysts in acidic environment, black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M HClO ₄ ,@0.7V vs RHE,900rpm).

detailed description

the term

As used herein, the term "linker molecule" or "linker group" refers to a modifying group attached to a carbon-based support by a covalent bond. Wherein, the "through a chemical bond" includes not only being directly connected to the surface of the carbon-based support through a covalent bond, but also including being connected with a modification group on the surface of the carbon-based support through a covalent bond.

As used herein, the term "alkyl" refers to a linear, branched or cyclic alkyl group having 1 to 30 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec Butyl, tert-butyl, cyclopropyl, or similar groups.

The term "C1-C4 alkyl" refers to a straight chain, branched or cyclic alkyl group with 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec Butyl, tert-butyl, cyclopropyl, or similar groups.

The term "aryl" refers to an aryl group having 6 to 30 carbon atoms, including monocyclic or bicyclic aryl groups such as phenyl, naphthyl, or the like.

The term "heteroaryl (heterocyclic aromatic group)" refers to a heteroaryl group having 2 to 30 carbon atoms, such as pyrrolyl, pyridyl, furyl, or the like.

The term "acylamino" refers to an amide group having 2 to 8 carbon atoms, such as acetamido, or the like.

The term "nitroaromatic group" refers to a nitrogen heterocyclic aromatic group having 2-30 carbon atoms, such as pyridine, pyrrole, or similar groups.

Unless otherwise specified, the term "substituted" means that one or more hydrogen atoms on the group are replaced by substituents selected from the group consisting of: C1～C10 alkyl, C1～C10 alkyl-oxyl, halogen, hydroxyl, carboxyl ( -COOH), C1～C10 alkyl-aldehyde group, C1～C10 alkyl-acyl group, C2～C10 ester group, cyano group, nitro group, amino group, phenyl group; the phenyl group includes unsubstituted phenyl or A substituted phenyl group having 1-3 substituents selected from the group consisting of: halogen, C1-C10 alkyl, cyano, OH, nitro, C1-C10 alkyl-oxyl, amino.

The term "polypyridyl" refers to a group having two or more pyridine ring structures in the structure, such as bipyridine or terpyridine.

The terms "carbon-based matrix support" or "carbon-based support" are used interchangeably to refer to the carrier of the present invention.

The names corresponding to the abbreviations are as follows:

Molecular oxygen reduction reaction catalyst

The compound of formula I can be used to catalyze the reduction reaction of oxygen molecules and prepare a catalyst for the reduction reaction of oxygen molecules.

A preferred class of base metal ORR catalysts of the present invention consists of carbon nanotubes with surface imidazole groups functionalized and biomimetic heme model metalloiron porphyrins. The imidazole groups on the surface of carbon nanotubes complete the covalent loading of biomimetic catalysts on carbon nanotubes through axial coordination with iron porphyrin. The invention realizes the functionalization of imidazole groups on the surface of carbon nanotubes, and is characterized in that after the functional modification of the monomolecular layer on the surface of carbon nanotubes, the effective assembly of the bionic heme model catalyst on the carbon nanotubes is realized, which greatly increases the carbon nanotube ORR active reaction sites on the surface of the tube, thereby greatly improving the ORR catalytic performance.

A preferred class of carbon-based supports are multi-walled carbon nanotubes.

A preferred class of linker molecules and coordination groups (Linker-Ligand) are:

A class of preferred iron porphyrins and derivatives thereof are:

In the formula, Ar is selected from the following group: substituted or unsubstituted C6-C30 aryl, substituted or unsubstituted C1-C30 heteroaryl. Preferably, the iron porphyrin derivative part has a structure as shown in Table 1:

Table 1 Iron-based porphyrin compounds

The invention realizes the functional modification of the imidazole group on the surface of the carbon nanotube and the covalent loading of the biomimetic ORR catalyst on the surface. The invention prepares an ORR base metal catalyst in a manner in which the catalyst structure is controllable and does not undergo high-temperature calcination. The ORR catalytic activity of the prepared catalyst is better than that of commercial platinum/carbon catalysts in both acidic and alkaline environments.

The main advantages of the present invention include:

(1) The structure of the catalyst prepared by the present invention is controllable, and the catalytic active center is clear.

(2) The performance of the catalyst prepared by the present invention is superior to all reported base metal ORR catalysts and commercial platinum/carbon catalysts. The ORR half-wave potential, ORR onset potential, ORR current density, and methanol poisoning resistance of the electrocatalyst prepared in the present invention are all better than commercial 20% platinum/carbon catalysts in acid and alkali environments.

(3) Since the catalytic performance of the ORR electrocatalyst of the present invention is superior to commercial 20% platinum/carbon catalysts, it may be used as a base metal ORR electrocatalyst to replace the existing precious metal platinum catalyst in the future, and has great potential in the fields of fuel cell electric vehicles and the like Application prospect and commercial value. New energy vehicle production companies may have potential demand for the invented technology.

Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. For the experimental methods without specific conditions indicated in the following examples, the conventional conditions or the conditions suggested by the manufacturer are usually followed. Percentages and parts are by weight unless otherwise indicated.

Example 1 Functional modification of imidazole groups on the surface of carbon nanotubes

Purified multi-walled carbon nanotubes (MWCNT, length ~ 50 μm, OD8-15nm, ID3-5nm, Chengdu Organic Chemical Co.Ltd, Chinese Academy of Sciences) and p-triisopropylsilylyl azofluorine The borate is ultrasonically dispersed in water, and a certain amount of hydrazine hydrate solution is added, heated to 80°C, and reacted overnight. The resulting filter cake was filtered and washed with DMF and ultrapure water, respectively.

Disperse a certain amount of triisopropylsilynylphenyl MWCNT in DMF, add tetrabutylammonium fluoride under ice-water bath, and react at room temperature under nitrogen atmosphere for 2 hours. Then, a certain amount of copper sulfate pentahydrate, sodium ascorbate and 1-(4-azidophenyl)imidazole were respectively added therein, and reacted at 50° C. for 36 hours under a nitrogen atmosphere. Filter the obtained filter cake, wash with DMF, 50mmol/LEDTA aqueous solution, and ultrapure water respectively to obtain imidazole-functionalized carbon nanotube MWCNTIm.

Example 2 Coordination loading of iron-based porphyrins on the surface of carbon nanotubes

Disperse 4.0 mg of modified MWCNTIm and 1.0 mg of iron porphyrin compound in 1.0 mL of methanol, and stir at room temperature for 15 h under nitrogen atmosphere. The complex was filtered, washed three times with a small amount of methanol, dried in vacuum for 3 h, and stored in a dark place under nitrogen atmosphere. The iron porphyrin is selected from the compounds listed in Table 1 above.

Embodiment 3 Catalyst performance test

(a) Preparation of catalyst ink (catalyst ink): an appropriate amount of 5% Nafion solution (Aldrich, USA) was ultrasonically mixed with isopropanol (volume ratio 1:9) for 5 min, and then an appropriate amount of the catalyst prepared by the present invention (CNTImFeF ₂ TPP , corresponding to the fourth compound in Table 1, R ₁ =R ₄ =R ₇ =F, R ₂ =R ₃ =R ₅ =R ₆ =H), ultrasonic dispersion is uniform. Take 10-15 μL of catalyst ink and drop it on the surface of the glassy carbon electrode, and use it as the working electrode after the solvent evaporates at room temperature.

(b) Electrochemical test of ORR catalytic performance:

The test of the electrocatalytic performance of the catalyst was realized by a rotating electrode device (MSR, product of Pine Company, USA) and a CHI760D electrochemical workstation. The test is completed in a three-electrode system (both products of Pine Company, USA), the glassy carbon electrode is the working disk electrode (OD: 5mm), the Pt ring is the working ring electrode (ID: 6.5mm, OD: 7.5mm), the Pt The wire is the counter electrode, and Hg/HgO (under alkaline conditions) or Ag/AgCl (under acidic conditions) is the reference electrode. The alkaline test environment is 0.1mol/L KOH solution, and the acidic test environment is 0.1mol/L HClO ₄ solution. The ORR measurement of the Pt-based catalyst as a control was done under the same conditions using a 20% Pt/C catalyst (JMHiSPEC3000, Johnson Matthey Fuel Cells, USA). The final potentials have been converted to potentials relative to the reversible hydrogen electrode (RHE).

The amount of catalyst supported on the surface of the glassy carbon electrode: the catalyst of the present invention: 1.0 mg/cm ² in total including carbon nanotubes, 0.2 mg/cm ² in iron porphyrin. Pt/C catalyst: 1.0 mg/cm ² .

The ORR polarization curves of the catalysts in alkaline environment are shown in Fig. 1. Black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M KOH, @1600rpm). The experimental results show that compared with the commercial 20%Pt/C catalyst, the ORR half-wave potential of the catalyst CNTImFeF ₂ TPP of the present invention shifts 50mV to the positive potential, and the ORR current density increases by about 20%.

Figure 2 shows the percentage of H ₂ O ₂ generated on the disk working electrode as a function of potential in an alkaline environment. Black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M KOH, @1600rpm). The experimental results show that the amount of H ₂ O ₂ generated by the catalyst CNTImFeF ₂ TPP of the present invention is only about half of that of the commercial 20%Pt/C catalyst, which shows that the catalyst of the present invention has a higher four-electron reduction selectivity for ORR, thus showing higher catalytic activity.

The stability of the catalyst in alkaline environment is shown in Fig. 3. Black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M KOH, @0.7V vs RHE, 900rpm). The experimental results show that the catalyst CNTImFeF ₂ TPP of the present invention still maintains about 96% of the catalytic activity after 25 hours, while the commercial 20%Pt/C catalyst only has about 55%.

The ORR polarization curve of the catalyst in acidic environment is shown in Figure 4, black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M HClO ₄ ,@1600rpm). The experimental results show that compared with the commercial 20%Pt/C catalyst, the ORR half-wave potential of the catalyst CNTImFeF ₂ TPP of the present invention shifts 36mV to the positive potential, and the ORR current density increases by about 20%.

The curve of the percentage of H ₂ O ₂ generated on the disk working electrode in an acidic environment versus the potential is shown in Figure 5. Black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M HClO ₄ ,@1600rpm). The experimental results show that the amount of H ₂ O ₂ generated by the catalyst CNTImFeF ₂ TPP of the present invention is less than that of the commercial 20%Pt/C catalyst, indicating that the catalyst of the present invention has a higher four-electron reduction selectivity for ORR, thereby showing a higher catalytic activity.

The stability test results of catalysts in acidic environment are shown in Figure 6, black solid line: 20%Pt/C; red solid line: CNTImFeF ₂ TPP (0.1M HClO ₄ ,@0.7V vs RHE,900rpm). The experimental results show that the catalyst CNTImFeF ₂ TPP of the present invention still maintains about 91% of the catalytic activity after 12.5 hours, while the commercial 20%Pt/C catalyst only has about 57%.

All documents mentioned in this application are incorporated by reference in this application as if each were individually incorporated by reference. In addition, it should be understood that after reading the above teaching content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims (9)

1. A composite catalyst having the structure:

Carrier-(Linker-Ligand-Metal complex)_nformula I

Wherein,

"-" represents a chemical bond, said chemical bond being a covalent bond or a coordinate bond;

carrier is carbon-based matrix Carrier;

ligand is a five-membered or six-membered heterocyclic coordination group containing nitrogen;

the Linker is a connecting molecule, and the connecting molecule is respectively connected with the carbon-based carrier and the nitrogen-containing five-membered or six-membered heterocyclic coordination group through a covalent bond; and the Linker has the following structure:

the Metal complex has iron-based porphyrin with the following structure:

wherein Ar is selected from the group consisting of: substituted or unsubstituted aryl, substituted or unsubstituted azacyclo aryl;

n≥1；

wherein said substitution means that one or more hydrogen atoms on the group are substituted with a substituent selected from the group consisting of: C1-C10 alkyl, C1-C10 alkyl-oxy, halogen, hydroxyl, carboxyl (-COOH), C1-C10 alkyl-aldehyde group, C1-C10 alkyl-acyl, C2-C10 ester group, cyano, nitro, amino and phenyl; the phenyl group includes an unsubstituted phenyl group or a substituted phenyl group having 1 to 3 substituents selected from: halogen, C1-C10 alkyl, cyano, OH, nitro, C1-C10 alkyl-oxy and amino.

2. The catalyst of claim 1, wherein the Carrier is selected from the group consisting of: single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene.

3. The catalyst of claim 1, wherein the Carrier is a multi-walled carbon nanotube.

4. The catalyst of claim 1, wherein Ligand is selected from the group consisting of: imidazolyl, pyridyl or polypyridyl.

5. The method of preparing a catalyst according to claim 1, comprising the steps of:

(i) providing a carbon-based Carrier with a connecting molecule and a nitrogen-containing five-membered or six-membered heterocyclic coordination group modified on the surface, wherein the connecting molecule Linker is connected to the surface of the carbon-based Carrier through a covalent chemical bond, and the nitrogen-containing five-membered or six-membered heterocyclic group Ligand is connected with the connecting molecule Linker through a covalent chemical bond;

Carrier-(Linker-Ligand)_mformula Ia

(ii) With substituted or unsubstituted Metal complex with said Carrier- (Linker-Ligand)_mCarrying out a reaction to form a compound shown as a formula I;

Carrier-(Linker-Ligand-Metal complex)_nformula I

Wherein, Carrier, Linker, Ligand, Metal complex, n are defined as the claim 1; m is greater than or equal to 1, and m and n can be equal or unequal.

6. The process of claim 5, wherein the compound of formula Ia is prepared by a process comprising the steps of:

providing a carbon-based Carrier;

carrying out surface modification on the carbon-based Carrier by using a coupling reagent to form a carbon-based Carrier with a connecting molecule modification on the surface;

the five or six membered heterocyclic group containing nitrogen is formed in situ on the linker molecule to give the compound of formula Ia.

7. Use of a catalyst according to any of claims 1 to 4 as a catalyst for the reduction of molecular oxygen.

8. An oxygen molecule reduction catalyst, wherein the catalyst comprises a catalyst according to any one of claims 1 to 4.

9. A fuel cell comprising a catalyst according to any one of claims 1 to 4.