CN110137518B

CN110137518B - Self-loading Fe-N-C oxygen reduction catalyst and preparation method thereof

Info

Publication number: CN110137518B
Application number: CN201910483401.XA
Authority: CN
Inventors: 严祥辉; 蒙紫薇; 黄红明; 房国丽; 许皓; 薛同; 沈宏芳
Original assignee: North Minzu University
Current assignee: North Minzu University
Priority date: 2019-06-04
Filing date: 2019-06-04
Publication date: 2022-05-17
Anticipated expiration: 2039-06-04
Also published as: CN110137518A

Abstract

The invention belongs to the technical field of non-noble metal catalysts in electrocatalysis, and particularly relates to an EDTAFeNa derived self-supported catalystA Fe-N-C supported oxygen reduction catalyst and a preparation method thereof. The mesoporous aperture of the self-supported Fe-N-C oxygen reduction catalyst is 3.9 +/-0.2 nm, and the specific surface area is 385 +/-2 m²g^‑1The content of Fe element is 0.4 +/-0.02 at.%, the content of N element is 2.6 +/-0.2 at.%, and the content of C element is 93 +/-2 at.%; the self-supported Fe-N-C oxygen reduction catalyst is obtained by mixing, evaporating and drying a mesoporous molecular sieve and sodium iron ethylene diamine tetraacetate, carrying out heat treatment under the protection of flowing gas, etching, carrying out acid treatment and carrying out heat treatment. The invention not only has high catalyst activity and selectivity, can realize high-efficiency electrocatalytic Oxygen Reduction Reaction (ORR) in alkaline electrolyte, but also has flexible preparation method route, large elastic space, controllable operation and easy large-scale production.

Description

Self-loading Fe-N-C oxygen reduction catalyst and preparation method thereof

Technical Field

The invention belongs to the technical field of non-noble metal catalysts in electrocatalysis, and particularly relates to an EDTAFeNa-derived self-supported Fe-N-C oxygen reduction catalyst and a preparation method thereof.

Background

The fuel cell can directly and efficiently convert chemical energy contained in fuel molecules into electric energy, only generates water which does not pollute the environment, and provides a new way for effectively utilizing the existing fossil energy. The novel power supply has the characteristics of light weight, high efficiency, quick start, long service life, low corrosivity, environmental friendliness and the like, and has a very great application prospect in the aspects of electric automobile power supplies, mobile power supplies, portable power supplies, power station applications and the like. Nevertheless, the realization of the civilian, commercial and industrial applications of fuel cells worldwide in a short period of time still faces a great challenge, wherein one of the key factors hindering the commercialization process is the low resource and high price of the electrode material (Pt or Pt-based catalyst) currently used by the fuel cells, which results in high cost of the fuel cells. To solve this problem, the development of inexpensive non-noble metal catalysts (NPMCs) that can replace Pt for fuel cell cathode oxygen reduction (ORR) is one of the important goals that researchers have been pursuing.

Disclosure of Invention

In order to solve the above problems, it is an object of the present invention to provide an EDTAFeNa-derived self-supported Fe-N-C oxygen reduction catalyst having a mesoporous structure, a large specific surface area, and a high degree of uniform nitrogen doping.

The invention also aims to provide a preparation method of the self-supported Fe-N-C oxygen reduction catalyst, which has the advantages of flexible synthetic route, large elastic space, controllable operation, relatively low cost and easy large-scale production.

The invention is realized by the following technical scheme:

the self-supported Fe-N-C oxygen reduction catalyst has a mesoporous aperture of 3.9 +/-0.2 nm and a specific surface area of 385 +/-2 m²g^-1The content of Fe element is 0.4 +/-0.02 at.%, the content of N element is 2.6 +/-0.2 at.%, and the content of C element is 93 +/-2 at.%;

the self-supported Fe-N-C oxygen reduction catalyst comprises a mesoporous molecular sieve and ethylenediaminetetraacetic acid iron sodium (EDTAFeNa), and the mass ratio of the mesoporous molecular sieve to the ethylenediaminetetraacetic acid iron sodium is 1: 1-20;

the mesoporous molecular sieve is one or a combination of SBA-15, MCM-41, MCM-48 or KIT-6. The mesoporous molecular sieve is used as a self-sacrificial hard template, and the EDTAFeNa has iron, nitrogen and carbon precursors.

The preparation method of the self-supported Fe-N-C oxygen reduction catalyst comprises the following steps:

1) firstly, adding a mesoporous molecular sieve into deionized water, then adding ethylenediamine tetraacetic acid ferric sodium salt for uniform dispersion, and then evaporating, drying and grinding the suspended matters to obtain solid powder A;

2) heating the A obtained in the step 1) to 650-750 ℃ at a speed of 10 +/-2 ℃/min under the protection of flowing inert gas, keeping for 1-3h, naturally cooling to room temperature, and grinding uniformly to obtain a catalyst precursor, wherein the label is EDTAFeNa-HT1 (MMS);

3) etching the catalyst precursor EDTAFeNa-HT1(MMS) obtained in the step 2) by using an ethanol aqueous solution of acid or alkali to obtain a desiliconized precursor EDTAFeNa-ET (MMS);

4) performing acid treatment on the EDTAFeNa-ET (MMS) obtained in the step 3) at 70-90 ℃ for 0.5-2M for 0.5-24 h, and performing suction filtration and drying to obtain a precursor EDTAFeNa-AL (MMS) with part of iron species removed;

5) subjecting the EDTAFeNa-AL (MMS) obtained in the step 4) to 180-220 mL min^-1Under the protection of flowing gas, heating to 600-1000 ℃ at the speed of 10 +/-2 ℃/min, keeping for 0.5-3 h, and then naturally cooling to room temperature, wherein the product at this stage is marked as EDTAFeNa-AL-HT2(MMS), namely the self-supported Fe-N-C catalyst. Among them, AL in EDTAFeNa-AL-HT2(MMS) is a self-naming, which indicates Acid treatment, and is an abbreviation of Acid-learning in English.

Preferably, the mesoporous molecular sieve and the ethylenediaminetetraacetic acid ferric sodium salt are added into the deionized water for dispersion, and the dispersion can be ultrasonic dispersion or solid phase mechanical mixing.

Preferably, in the step 1), other nitrogen-containing small molecular compounds can be added at the same time; the nitrogen-containing small molecular compound is one or a composition of melamine, urea, pyrrole and ethylenediamine.

Preferably, in the step 1), activating agents KOH and K can be added simultaneously₂CO₃、(NH₄)₂CO₃、ZnCO₃A combination of one or more of (a).

Preferably, the flowing sex gas is N₂Or He.

Preferably, in step 3), etching is performed with an ethanol aqueous solution of an acid or an alkali, specifically: adding EDTAFeNa-HT1(MMS) into an ethanol-water solution of NaOH with the molar concentration of 1.5-2.5M, stirring for 20-25 h at 55-65 ℃, then repeatedly washing for 3 times by using deionized water and ethanol, carrying out suction filtration and drying; the volume ratio of ethanol to water in the ethanol-water solution is 1: 1. When etching is performed with an aqueous ethanol solution of an acid, HF is preferable.

Preferably, the acid in the acid treatment in the step 4) is HCl or H₂SO₄Or HNO₃And (3) solution.

Preferably, in step 5), the flowing gas is an inert gas or a reactive gas NH₃。

In the traditional preparation method of the Fe-N-C material based on the carbon carrier, the nitrogen-containing precursor and the metal salt, because the nitrogen-containing precursor is degraded and carbonized in the heat treatment process, the carbon carrier is not uniformly doped with N, and the pore channels of the carbon carrier are inevitably blocked to different degrees, a balance compromise always exists among several key factors influencing ORR, such as pore diameter, specific surface area, active site density and distribution.

The invention adopts the ordered mesoporous molecular sieve as a sacrificial hard template, aims to cut out a mesoporous Fe-N-C material with large specific surface area by utilizing the mesoscopic structure of the mesoporous molecular sieve, is beneficial to the exposure of active sites and the mass transfer diffusion of bottom products, improves the electron transfer rate, and also aims to improve the carbonization yield and reduce the loss of N element by the interaction of rich pore channels and EDTAFeNa; the only cheap organic-inorganic compound EDTAFeNa is selected to combine with Fe, N and C precursors, so that the raw material cost can be reduced, and the structural complexity caused by the interaction of multi-component precursors can be avoided; in addition, the Fe and N co-doped carbon material can be obtained only by cracking one precursor of EDTAFeNa, and the self-doping is expected to obtain more uniformly distributed active sites and improve the density of the active sites; the acid treatment can remove inactive Fe species and further regulate the mesostructure of the material; thereby synergizing a non-noble metal catalyst with excellent ORR activity.

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

1) the preparation process only uses a cheap organic-inorganic compound EDTAFeNa which has Fe, N and C precursors;

2) in the preparation process, SBA-15 is used as a hard template and is combined with acid treatment, so that the N doping and graphitization degree can be effectively improved, narrow-distribution mesopores and large specific surface area are created, the non-activity is removed, or the 2e of ORR is promoted to occur^-Crystalline Fe species of selective reaction pathway, thus capable of being species and electrons of ORR processThe fast transmission of (1) provides a channel;

3) under the alkaline condition, the self-supported mesoporous Fe-N-C material catalyzes the initial and half-wave potentials of ORR and has the kinetic current density close to that of a commercial Pt/C catalyst under the high potential, and catalyzes the ORR to have high energy conversion efficiency^-The reaction path is carried out;

4) the catalyst has wide application range and can be used as cathode oxygen reduction catalyst of various fuel cells.

The method for preparing the EDTAFeNa-derived self-supported Fe-N-C catalyst has the advantages of low reagent toxicity, safety, environmental protection, few components, low raw material cost, flexible preparation process, large elastic space, controllable operation, high yield and easiness in large-scale production in the preparation process.

Drawings

FIG. 1 shows N of EDTAFeNa-HT2, EDTAFeNa-HT1 and EDTAFeNa-AL₂Adsorption/desorption isotherms and pore size distribution.

FIG. 2 shows hysteresis curves for EDTAFeNa-HT2, EDTAFeNa-HT1 and EDTAFeNa-AL.

FIG. 3 is a TEM photograph of EDTAFeNa-HT 2.

FIG. 4 is a statistical distribution diagram of Fe species size in TEM photographs of EDTAFeNa-HT 2.

FIG. 5 is a small angle XRD spectrum of EDTAFeNa-HT2(SBA-15) and EDTAFeNa-AL-HT2 (SBA-15).

FIG. 6 is a wide angle XRD spectrum of EDTAFeNa-HT2(SBA-15) and EDTAFeNa-AL-HT2 (SBA-15).

FIG. 7 shows the N of EDTAFeNa-HT2(SBA-15) and EDTAFeNa-AL-HT2(SBA-15)₂Adsorption/desorption isotherms and pore size distributions.

FIG. 8 is an XPS survey of EDTAFeNa-HT2(SBA-15) and EDTAFeNa-AL-HT2 (SBA-15).

FIG. 9 shows hysteresis curves of EDTAFeNa-HT2(SBA-15) and EDTAFeNa-AL-HT2 (SBA-15).

FIG. 10 is a graph at O₂Polarization curves for EDTAFeNa-HT2(SBA-15), EDTAFeNa-AL-HT2(SBA-15) and Pt/C catalyzed ORR in saturated 0.1M KOH (room temperature, sweep speed 10mV s)^-11600 rpm).

FIG. 11 is a plot of the polarization of the ORR catalyzed by EDTAFeNa-HT2(SBA15) at different rotational speedsLine and each O at different potentials₂The number of electrons that the molecule undergoes a reaction transfer.

FIG. 12 is a polarization curve of the catalytic ORR of EDTAFeNa-AL-HT2(SBA15) at different speeds and for each O at different potentials₂The number of electrons that the molecule undergoes a reaction transfer.

Detailed Description

The present invention is described in further detail below with reference to specific embodiments to assist those skilled in the art in understanding the present invention.

Example 1

1) 2g of EDTAFeNa is put into a quartz boat and placed in a tube furnace for 200mL min^-1 N₂Under protection, heating to 700 ℃ at the speed of 10 ℃/min, keeping for 2h, naturally cooling to room temperature, and then grinding uniformly, wherein the product at this stage is named as EDTAFeNa-HT 1.

2) Collecting 0.25g EDTAFeNa-HT1, 30ml of 0.5M H at 80 deg.C₂SO₄And (3) carrying out acid treatment in the solution for 0.5h, carrying out suction filtration and drying after the acid treatment is finished, and naming the product at this stage as EDTAFeNa-AL.

3) Taking 0.15g EDTAFeNa-AL and continuing to perform 200mL min^-1 N₂Under protection, heating to 900 ℃ at the speed of 10 ℃/min and keeping for 2 hours, then naturally cooling to room temperature, grinding uniformly for later use, and marking a sample obtained at the stage as EDTAFeNa-HT 2.

This preparation was carried out without using SBA-15 as a hard template, but using an acid treatment step, and compared as a control catalyst with a catalyst prepared by acid treatment while using SBA-15 as a hard template, as described below.

N of EDTAFeNa-HT2 synthesized in this example₂The absorption/desorption isotherms and pore size distributions and hysteresis curves are shown in fig. 1 and 2; TEM (transmission electron microscopy) and statistical distribution of Fe species sizes are shown in FIGS. 3 and 4.

Example 2

1) 0.4g of self-made SBA-15 is added into 45mL of deionized water, 7.88g of EDTAFeNa is added, magnetic stirring is carried out for 0.5h, ultrasonic dispersion is carried out for 2h, and then the suspended matters are evaporated, dried and ground to obtain solid powder A.

2) A sample of 1g A was taken at 200mLmin^-1 N₂Under protection, heating to 700 ℃ at the speed of 10 ℃/min, keeping for 1-3h, then naturally cooling to room temperature, and grinding uniformly to obtain a catalyst precursor, namely EDTAFeNa-HT1 (SBA-15).

3) 0.25g of EDTAFeNa-HT1(SBA-15) was added to 25mL of 2M NaOH in ethanol-water (1: 1, V: V) solution, stirred at 60 ℃ for 24h, and then washed 3 times with deionized water and ethanol, filtered with suction, and dried, and the alkali etching process was performed to remove the SBA-15 template from the sample, to obtain a desilicated precursor C, named EDTAFeNa-ET (SBA-15).

4) Taking 0.15g EDTAFeNa-ET (SBA-15), and dissolving in 200mL min^-1 N₂Under protection, the temperature is raised to 900 ℃ at the speed of 10 ℃/min and kept for 2h, and then the product is naturally cooled to room temperature, and the product at this stage is marked as EDTAFeNa-HT2 (SBA-15).

This preparation uses SBA-15 as a hard template, but does not use H₂SO₄The solution was acid treated and still used as a control catalyst to compare with the catalyst prepared by acid treatment using SBA-15 as a hard template as described below.

Example 3

The experimental procedure was the same as in example 2, except that a single acid treatment was added between experimental procedures 3) and 4), and the experimental procedure was the same as in experimental procedure 2) of example 1, and the finally obtained sample was named EDTAFeNa-AL-HT2 (SBA-15).

The small-angle and wide-angle XRD spectra of EDTAFeNa-AL-HT2(SBA-15) synthesized in this example and EDTAFeNa-HT2(SBA-15) synthesized in example 2 are shown in FIGS. 5 and 6; n is a radical of₂The adsorption/desorption isotherms, pore size distributions and texture parameters are shown in fig. 7 and table 1; XPS full spectrum and surface elemental composition are shown in figure 8 and table 2; the hysteresis curve is shown in fig. 9.

Example 4

3mg of the self-supported Fe-N-C catalyst prepared in examples 1, 2 and 3 was weighed, dispersed in 0.5mL of a mixed solution of 5 wt% Nafion and deionized water (1/9, V/V), ultrasonically dispersed for 1h, then 15. mu.L of the uniformly dispersed catalyst suspension was transferred and coated on the surface of a polished glassy carbon electrode, dried under an infrared lamp, used as a working electrode after the solvent was completely volatilized, and then used as a counter electrode with a platinum wire and an Ag/AgCl electrode as a reference electrode to test the ORR activity of the material in 0.1M KOH by CV, LSV electrochemical methods.

Example 5

A self-supported Fe-N-C oxygen reduction catalyst is prepared by the following method:

1) adding 0.4g of SBA-15 into 45mL of deionized water, adding 7.88g of EDTAFeNa, magnetically stirring for 0.5h, ultrasonically dispersing for 2h, and then evaporating, drying and grinding the suspended substance to obtain solid powder A.

2) Taking 1g A sample, at 200mL min^-1 N₂Raising the temperature to 700 ℃ at a speed of 5 ℃/min for 2.5h under protection, then naturally cooling to room temperature, and uniformly grinding to obtain a catalyst precursor, which is marked as EDTAFeNa-HT1 (SBA-15).

4) 0.25g of EDTAFeNa-ET (SBA-15) was taken at 80 ℃ and 30ml of 0.5M H₂SO₄Acid treatment is carried out on the solution for 0.5h, suction filtration and drying are carried out after the acid treatment is finished, and the product at this stage is named as EDTAFeNa-AL (SBA-15).

5) Collecting 0.15g EDTAFeNa-AL (SBA-15) at 200mL min^-1 N₂Under protection, the temperature is raised to 900 ℃ at the speed of 10 ℃/min and kept for 2h, and then the product is naturally cooled to room temperature, and the product at this stage is marked as EDTAFeNa-AL-HT2(SBA-15), namely the self-loading Fe-N-C catalyst.

Example 6

1, adding 0.4g of MCM-48 into 45mL of deionized water, adding 6g of EDTAFeNa, magnetically stirring for 2h, mechanically mixing and dispersing a solid phase for 2h, and then evaporating, drying and grinding the suspended substance to obtain solid powder A.

2) Taking 1g A sample, at 200mL min^-1Under the protection of He, raising the temperature to 650 ℃ at 15 ℃/min and keeping the temperature for 3h, then naturally cooling to room temperature and uniformly grinding to obtain a catalyst precursor, which is marked as EDTAFeNa-HT1 (MCM-48).

3) 0.25g of EDTAFeNa-HT1(MCM-48) was added to 25mL of 2M NaOH in ethanol-water (1: 1, V: V) solution, stirred at 55 ℃ for 24h, and then washed 3 times with deionized water and ethanol, filtered, and dried, and the alkaline etching process was performed to remove the MCM-48 template in the sample, to obtain a desilicated precursor C, named EDTAFeNa-ET (MCM-48).

4) Collecting 0.25g EDTAFeNa-ET (MCM-48) at 75 deg.C and 30ml 2M HNO₃Acid treatment is carried out on the solution for 0.5h, suction filtration and drying are carried out after the acid treatment is finished, and the product at the stage is named as EDTAFeNa-AL (MCM-48).

5) Collecting 0.15g EDTAFeNa-AL (MCM-48) in 200mL min^-1 NH₃Under protection, the temperature is raised to 950 ℃ at the speed of 10 ℃/min and kept for 2h, and then the product is naturally cooled to room temperature, and the product at this stage is marked as EDTAFeNa-AL-HT2(MCM-48), namely the self-loading Fe-N-C catalyst.

Example 7

1) adding 0.4g of KIT-6 into 45mL of deionized water, adding 7.88g of EDTAFeNa, magnetically stirring for 0.5h, ultrasonically dispersing for 2h, and then evaporating, drying and grinding the suspended substance to obtain solid powder A.

2) Taking 1g A sample, at 200mL min^-1 N₂Raising the temperature to 750 ℃ at a speed of 10 ℃/min for 1h under protection, then naturally cooling to room temperature, and uniformly grinding to obtain a catalyst precursor, which is marked as EDTAFeNa-HT1 (KIT-6).

3) 0.25g of EDTAFeNa-HT1(KIT-6) was added to 25mL of 2M NaOH in ethanol-water (1: 1, V: V) and stirred at 70 ℃ for 24h, then washing with deionized water and ethanol was repeated 3 times, suction filtration and drying, and the alkali etching process was performed to remove the KTT-6 template from the sample to obtain the desilicated precursor C, named EDTAFeNa-ET (KIT-6).

4) 0.25g of EDTAFeNa-ET (KIT-6) is taken to be subjected to acid treatment for 0.5h in 30ml of 0.5M HC1 solution at 75 ℃, suction filtration and drying are carried out after the acid treatment is finished, and the product at this stage is named as EDTAFeNa-AL (KIT-6).

5) Collecting 0.15g EDTAFeNa-AL (KIT-6) in 200mL min^-1 N₂Under protection, the temperature is raised to 900 ℃ at the speed of 10 ℃/min and kept for 2h, and then the temperature is naturally cooled to room temperature, and the product at this stage is marked as EDTAFeNa-AL-HT2(KIT-6), namely the self-loading Fe-N-C catalyst.

In the examples of the present invention, commercial 20% Pt/C for comparison was Johnson Matthey corporation. Unless otherwise stated, the characterization and electrochemical testing methods used in the examples are conventional in the art.

TABLE 1 structural Property parameters of self-supporting Fe-N-C oxygen reduction catalysts

TABLE 2 surface elemental composition of self-supporting Fe-N-C oxygen reduction catalysts

TABLE 3 Activity parameters for self-supporting Fe-N-C oxygen reduction catalysts to catalyze ORR in 0.1M KOH

As can be seen from tables 1-3, the self-supported Fe-N-C catalyst has narrow mesoporous pore size distribution (3.9 nm) and large specific surface area (385 m)² g^-1) High degree of graphitization, higher N content and low surface Fe content (< 0.5 at.%). Both the onset and half-wave potentials were only 10mV lower than commercial Pt/C catalyst (JM, 20 wt% Pt).

Polarization curves for the series of self-supported Fe-N-C catalysts and Pt/C catalysts prepared in examples 1, 2, 3 catalyzed ORR and the initial potentials obtained (E)_onset) Half-wave potential (E)_1/2) Limiting current density (J)_L) And dynamic Current Density (J)_k) As shown in fig. 10 and table 3; polarization curves of ORR at different rotation speeds on EDTAFeNa-HT2(SBA-15) prepared in example 2 and EDTAFeNa-AL-HT2(SBA-15) prepared in example 3 and the corresponding K-L equation fit lines (inset) at different potentials are shown in FIGS. 11 and 12, respectively.

FIGS. 1 and 2 show the N of the three-stage product of example 1, EDTAFeNa- (HT1, AL, HT2)₂The absorption and desorption curve, the pore size distribution and the hysteresis curve are combined with the texture parameters in the table 1, which shows that acid treatment can effectively remove a large amount of magnetic Fe species, and simultaneously the mesostructure of the sample is regulated and controlled to obtain the product with larger specific surface area (more than 220 m)² g^-1) The micro-mesoporous material of (1). Fig. 3 and 4 show TEM photographs of the product of example 1, edtafenia-HT 2, and the statistical distribution of the sizes of the Fe species produced, and it can be seen that the remaining Fe species are encapsulated in the graphene or graphite structure, and the particle size is in the nanometer range, indicating that cracking only edtafenia one precursor in combination with acid treatment can suppress to some extent the particle size increase caused by aggregation of the Fe species generated and remove the surface Fe species. FIGS. 5, 6, 7, 8 and 9 show the low angle, wide angle XRD patterns, N-15, of EDTAFeNa-HT2(SBA-15) and EDTAFeNa-AL-HT2(SBA-15) synthesized in examples 2 and 3, respectively₂The results of the absorption/desorption isotherms, pore size distributions, XPS full spectra and hysteresis curves combined with the data in tables 1 and 2 demonstrate that mesoporous Fe-N-C materials with a certain degree of order, large specific surface area, narrow pore size distribution, high graphitization degree and high N content can be cut out by using the ordered mesoporous molecular sieve SBA-15 as a sacrificial hard template and simultaneously treating with acid, and almost all crystalline iron species such as alpha-Fe, Fe₃C and Fe₃O₄Can be removed.

FIGS. 10, 11, 12 and Table 3 show the final stages of synthesis of examples 1, 2 and 3, respectively, for 3 samples and the Pt/C catalyst at O₂Electrochemical Performance of catalytic ORR in saturated 0.1M KOHThe results showed that EDTAFeNa-AL-HT2(SBA-15) synthesized in example 3 has the highest catalytic performance on ORR, and E thereof_onset、E_1/2、J_LAnd J_k(0.87V) respectively up to 0.96V, 0.83V and 4.20mA cm^-2And 1.32mA cm^-2E with Pt/C only_onsetAnd E_1/2The difference is 10mV, and the catalysis ORR is carried out by a 4-electron reaction path, so that the mesostructure, the high graphitization degree and the high N content of an obtained EDTAFeNa-AL-HT2(SBA-15) by taking SBA-15 as a hard template and taking a cheap organic-inorganic compound EDTAFeNa as a precursor with Fe, N and C are beneficial to the exposure of an active site, the mass transfer diffusion of a bottom product and the increase of the density of the active site, thereby improving the electron transfer rate and leading to the improvement of the ORR activity; in addition, the synthesis method of the EDTAFeNa-HT2(SBA-15) and the EDTAFeNa-AL-HT2(SBA-15) catalytic ORR synthesized in the comparative examples 2 and 3 can reduce the cost of raw materials, has the characteristics of flexible process route, large elastic space, controllable operation and the like, and has great potential to cooperate with a non-noble metal catalyst with more excellent activity on ORR under optimized preparation conditions.

Claims

1. The self-supported Fe-N-C oxygen reduction catalyst is characterized in that the mesoporous aperture of the self-supported Fe-N-C oxygen reduction catalyst is 3.9 +/-0.2 nm, and the specific surface area is 385 +/-2 m²g^-1The content of Fe element is 0.4 +/-0.02 at.%, the content of N element is 2.6 +/-0.2 at.%, and the content of C element is 93 +/-2 at.%;

the raw materials of the self-supported Fe-N-C oxygen reduction catalyst comprise a mesoporous molecular sieve and sodium iron ethylene diamine tetraacetate, and the mass ratio of the mesoporous molecular sieve to the sodium iron ethylenediamine tetraacetate is 1: 1-20; the mesoporous molecular sieve is one or a combination of SBA-15, MCM-41, MCM-48 or KIT-6; the preparation method of the self-supported Fe-N-C oxygen reduction catalyst is characterized by comprising the following steps of:

1) firstly, adding a mesoporous molecular sieve into deionized water, and then adding ethylenediaminetetraacetic acid ferric sodium salt for uniform dispersion to obtain suspended matters; then evaporating, drying and grinding the suspended substance to obtain solid powder A;

2) heating the A obtained in the step 1) to 650-750 ℃ at a speed of 10 +/-2 ℃/min under the protection of flowing inert gas, keeping for 1-3h, naturally cooling to room temperature, and grinding uniformly to obtain a catalyst precursor, wherein the catalyst precursor is marked as EDTAFeNa-HT1(MMS), and MMS is an English abbreviation of mesoporous molecular sieve and is a composition of one or more of SBA-15, MCM-41, MCM-48 or KIT-6;

4) carrying out acid treatment on the EDTAFeNa-ET (MMS) obtained in the step 3) in a 0.5-2M solution at 70-90 ℃ for 0.5-24 h, and carrying out suction filtration and drying after the acid treatment to obtain a precursor EDTAFeNa-AL (MMS) with part of iron species removed;

5) subjecting the EDTAFeNa-AL (MMS) obtained in the step 4) to 180-220 mL min^-1Under the protection of flowing gas, heating to 600-1000 ℃ at the speed of 10 +/-2 ℃/min, keeping for 0.5-3 h, and then naturally cooling to room temperature, wherein the product at this stage is marked as EDTAFeNa-AL-HT2(MMS), namely the self-supported Fe-N-C oxygen reduction catalyst:

in the step 3), etching is performed by using an ethanol aqueous solution of acid or alkali, specifically: adding EDTAFeNa-HT1(MMS) into an ethanol-water solution of NaOH with the molar concentration of 1.5-2.5M, stirring at 55-65 ℃ for 20-25 h, then repeatedly washing with deionized water and ethanol for 3 times, filtering, and drying; the volume ratio of ethanol to water in the ethanol-water solution is 1: 1.

2. The method for preparing a self-supported Fe-N-C oxygen reduction catalyst according to claim 1, wherein in the step 1), the mesoporous molecular sieve and the ferric sodium ethylene diamine tetraacetate are added into the deionized water in a dispersion mode of ultrasonic dispersion or solid phase mechanical mixing.

3. The method for preparing a self-supported Fe-N-C oxygen reduction catalyst according to claim 1, wherein in the step 1), other nitrogen-containing small molecular compounds are added at the same time; the nitrogen-containing small molecular compound is one or a composition of melamine, urea, pyrrole and ethylenediamine.

4. The method for preparing a self-supported Fe-N-C oxygen reduction catalyst according to claim 1, wherein KOH and K are added simultaneously in the step 1)₂CO₃、(NH₄)₂CO₃、ZnCO₃A combination of one or more of (a).

5. The method of preparing a self-supported Fe-N-C oxygen reduction catalyst as claimed in claim 1 wherein in step 2) the flowing inert gas is He.

6. The method for preparing a self-supported Fe-N-C oxygen reduction catalyst according to claim 1, wherein in the step 3), the etching is performed by using an ethanol aqueous solution of acid or alkali, specifically: adding EDTAFeNa-HT1(MMS) into an ethanol-water solution of HF with the molar concentration of 1.5-2.5M, stirring for 20-25 h at 55-65 ℃, then repeatedly washing for 3 times by using deionized water and ethanol, carrying out suction filtration, and drying.

7. The method for preparing a self-supported Fe-N-C oxygen reduction catalyst according to claim 1, wherein in the step 4), the acid in the acid treatment is HC1, H₂SO₄Or HNO₃And (3) solution.

8. The method of claim 1, wherein in step 5), the flowing gas is an inert gas or an active gas NH₃。