CN109449448B

CN109449448B - Fuel cell cathode catalyst and preparation method and application thereof

Info

Publication number: CN109449448B
Application number: CN201811223442.7A
Authority: CN
Inventors: 周瑜; 王宗花; 张艳
Original assignee: Qingdao University
Current assignee: Qingdao University
Priority date: 2018-10-19
Filing date: 2018-10-19
Publication date: 2021-04-02
Anticipated expiration: 2038-10-19
Also published as: CN109449448A

Abstract

The invention relates to a fuel cell cathode catalyst and a preparation method and application thereof, wherein 2-amino-terephthalic acid and iron salt are used as raw materials, a solvothermal synthesis method is adopted to prepare a metallic iron-organic framework material, the metallic iron-organic framework material is washed for three times by using N, N-dimethylformamide and then filtered, the filtered precipitate is dried to obtain a precursor, the precursor is roasted at 550-650 ℃ in an inert gas atmosphere, and then acid treatment is carried out to obtain a nitrogen-iron doped carbon nano material, wherein the solvent adopted by the solvothermal synthesis method is an N, N-dimethylformamide organic solvent. The nitrogen-iron doped carbon nano material prepared by the preparation method has excellent oxygen reduction catalytic activity, better initial potential and limiting current and stable methanol resistance, and the electron transfer number of the nitrogen-iron doped carbon nano material is close to that of a four-electron transfer way.

Description

Fuel cell cathode catalyst and preparation method and application thereof

Technical Field

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

Background

The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.

In view of the ever-increasing energy demand, emerging energy conversion devices are becoming hot spots. For example, new electrochemical energy conversion devices have shown great application prospects to meet the ever-increasing energy needs of people. In the research on the existing fuel cell, the oxygen reduction catalyst of the fuel cell includes a noble metal catalyst, a non-noble metal catalyst, a carbon-based non-metal catalyst, and the like. Wherein the noble metal catalyst mainly comprises platinum, palladium and the like, and has the defect of higher price; the non-noble metal catalyst mainly comprises iron, cobalt and the like, and has the defect of poor stability; the applicant previously proposed a non-metallic porous carbon catalyst in CN 108281679 a, which has a certain disadvantage in catalytic performance although having good stability, and further requires a long time (5 ± 0.5h) for boiling to remove water molecules or unreacted ligands remaining in the pores, which is time-consuming and energy-consuming, further limiting its commercial large-scale use. Therefore, it is important to search for a new electrochemical material with high efficiency.

Disclosure of Invention

In view of the above background, the present disclosure provides a fuel cell cathode catalyst, a method of preparing the same, and applications thereof. Compared with a nitrogen-doped carbon nano material in CN 108281679A, the fuel cell cathode catalyst prepared by the method has better oxygen reduction catalytic activity, better initial potential and limiting current, better stability and methanol resistance, and the electron transfer number of the fuel cell cathode catalyst is closer to a four-electron transfer path.

The present disclosure specifically adopts the following technical scheme:

first, the present disclosure provides a method for preparing a fuel cell cathode catalyst, the method comprising the steps of:

the preparation method comprises the steps of taking 2-amino-terephthalic acid and ferric salt as raw materials, preparing a metallic iron-organic framework material by adopting a solvothermal synthesis method, placing the metallic iron-organic framework material in N, N-dimethylformamide for washing, filtering, drying a filtered precipitate to obtain a precursor, roasting the precursor at 550-650 ℃ in an inert gas atmosphere, and then carrying out acid treatment to obtain the nitrogen-iron doped carbon nanomaterial, wherein the solvent adopted by the solvothermal synthesis method is an N, N-dimethylformamide organic solvent.

The disclosure also protects the nitrogen-iron doped carbon nanomaterial prepared by the method and application of the nitrogen-iron doped carbon nanomaterial in preparation of a fuel cell cathode catalyst.

Secondly, a fuel cell is provided, which is characterized in that: the nitrogen-iron doped carbon nanomaterial is used as a fuel cell cathode catalyst.

In addition, the application of the nitrogen-iron doped carbon nanomaterial in electrocatalysis is provided.

Compared with the related technology known by the inventor, one technical scheme of the present disclosure has the following beneficial effects:

the method prepares the nanoscale metallic iron-organic framework material by a direct solvothermal method, and prepares the nitrogen-iron doped carbon nanomaterial catalyst material by taking the metallic iron-organic framework material as a precursor through high-temperature carbonization. Compared with the nitrogen-doped carbon nanomaterial in the prior CN 108281679A, the fuel cell cathode catalyst disclosed by the disclosure has better catalytic performance, is closer to an ideal four-electron transfer reaction, and also has better methanol resistance and stability. The non-noble metal carbon material oxygen reduction catalyst synthesized by the method has important prospects in development and application in the aspect of fuel cells. Moreover, compared with the nitrogen-doped carbon nanomaterial in CN 108281679A, the preparation process is short in time consumption and low in energy consumption.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate embodiments of the disclosure and, together with the description, serve to explain the disclosure and not to limit the disclosure.

Fig. 1 is an electron microscope picture in which a: scanning electron micrograph of N-C-Fe-600 precursor, b: scanning electron micrograph of N-C-Fe-600, C: transmission electron micrograph of N-C-Fe-600 precursor, d: transmission electron micrograph of N-C-Fe-600.

Fig. 2 is an XRD spectrum, in which a: XRD spectrum of precursor, b: is an XRD spectrum of N-C-Fe-600.

FIG. 3 is a high resolution XPS spectrum of N-C-Fe-600, wherein a: element type spectrum, b: high resolution XPS spectrum of C1s, C: N1s, d: Fe2 p.

FIG. 4 is a Raman spectrum of N-C-Fe-600.

FIG. 5 is a BET spectrum of N-C-Fe-600.

FIG. 6 is a thermogravimetric plot of a precursor of N-C-Fe-600.

FIG. 7 shows the oxygen saturation of 0.1 mol.L for materials at different temperatures^-1Linear sweep profile in KOH solution.

In fig. 8, a: the scanning speed of the N-C-Fe-600 modified electrode is 50mV & s^-1Cyclic voltammetry of (a); b: linear sweep curve and ring disk electrode test curve of N-C-Fe-600 at 1600rpm, sweep speed of 5 mV. multidot.s^-1(ii) a c: linear scanning curves of N-C-Fe-600 at different rotating speeds; d: Koutecky-Le of N-C-Fe-600vich (K-L) curve.

FIG. 9 shows the N-C-Fe-600 modified electrode and commercial Pt/C at 0.1 mol. L saturated with oxygen^-1Stability test in KOH solution (a) and methanol resistance test (b).

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, and/or combinations thereof, unless the context clearly indicates otherwise.

The iron salt is a compound which is dissolved in water and can ionize iron ions, such as ferric chloride, ferric sulfate, ferric nitrate and the like.

The solvothermal synthesis method is a chemical reaction which is carried out in a sealed pressure container under the conditions of high temperature and high pressure by taking N, N-dimethylformamide as a mixture of an organic solvent and water as a solvent.

The inert gas refers to a gas which is difficult to generate combustion reaction with organic matters or carbon, such as nitrogen, argon and the like.

As introduced in the background art, the prior art has the defects of high price of a noble metal catalyst and poor stability of a non-noble metal catalyst, and in order to solve the technical problems, the application provides the preparation of a nitrogen-doped carbon nano material and the application of the nitrogen-doped carbon nano material in electrocatalytic oxygen reduction.

As described in the background art, the catalytic performance of the non-metal catalyst in CN 108281679 a is not enough, and in order to solve the above technical problems, the present disclosure provides a method for preparing a cathode catalyst of a fuel cell, the method comprising the following steps:

the preparation method comprises the steps of taking 2-amino-terephthalic acid and ferric salt as raw materials, preparing a metallic iron-organic framework material by adopting a solvothermal synthesis method, placing the metallic iron-organic framework material in N, N-dimethylformamide for washing, filtering, drying a filtered precipitate to obtain a precursor, roasting the precursor at 550-650 ℃ in an inert gas atmosphere, and then performing acid treatment to obtain the nitrogen-iron doped carbon nanomaterial. Wherein, the solvent adopted in the solvothermal synthesis method is N, N-dimethylformamide.

The crystal morphology obtained by adopting different solvents in the solvothermal reaction is different. DMF is selected, so that the obtained nitrogen-iron doped carbon nano material matrix is in a polyhedral granular shape.

In one or some specific embodiments of the present disclosure, the molar ratio of 2-amino-terephthalic acid to iron salt is 1: 1.

In one or some specific embodiments of the present disclosure, the addition ratio of the 2-amino-terephthalic acid to N, N-dimethylformamide is (1-2) mmol: (25-35) mL.

In one or some embodiments of the present disclosure, 2-amino-terephthalic acid and iron salt are dissolved in N, N-dimethylformamide, and the 2-amino-terephthalic acid solution is mixed with the iron salt solution and then reacted using a solvothermal synthesis method.

Further, 1.3838mmol of 2-amino-terephthalic acid and 1.3838mmol of iron salt are dissolved in 30mL of N, N-dimethylformamide solution, and the 2-amino-terephthalic acid solution and the iron salt solution are mixed and then react by a solvothermal synthesis method.

In one or more specific embodiments of the present disclosure, the solvothermal synthesis temperature is 110-130 ℃, and the synthesis time is 19-21 h. If the temperature is high or low, the crystallization degree of the obtained material is not good; further, the temperature of solvothermal synthesis was 120 ℃.

In one or some specific embodiments of the present disclosure, the inert gas is argon.

In the disclosureIn one or more specific embodiments, the temperature rise rate of the roasting is 2-4 ℃ min^-1More preferably 3 ℃ min^-1。

In one or more specific embodiments of the present disclosure, the baking time is 3 to 4 hours.

The roasting temperature not only influences the change of iron in the nitrogen-iron doped carbon nano material, but also influences the structure and the micro-morphology of the iron doped carbon nano material, thereby influencing the catalytic performance of the fuel cell cathode catalyst. In one or more specific embodiments of the present disclosure, the roasting temperature is 595-605 ℃; further, the roasting temperature is 600 ℃.

In one or some embodiments of the present disclosure, the filtered precipitate is dried after three washes. Further, washing was performed with an N, N-dimethylformamide solution.

And (3) washing by adopting N, N-Dimethylformamide (DMF) for multiple times to remove unreacted ligands remained in the holes, and meanwhile, not dissolving the metallic iron-organic framework material, so that the material structure is prevented from being damaged, and the activation effect is achieved. In CN 108281679A, boiling (5 + -0.5 h) is required for a long time to remove the water molecules or unreacted ligands remained in the pores, otherwise, the water molecules or unreacted ligands doped in the pores can affect the catalytic stability and methanol resistance of the material.

In one or some specific embodiments of the present disclosure, the drying is vacuum drying. The drying time is 11-13 h.

In one or some specific embodiments of the present disclosure, the acid used for the acid treatment is hydrochloric acid. Further, the concentration of hydrochloric acid was 2M.

In an exemplary embodiment of the present disclosure, there is provided a nifro-doped carbon nanomaterial obtained by the above-described preparation method. The material is a nitrogen and iron doped porous carbon material, has relatively uniform pore distribution, and the size of pores is about 19 nm; the microscopic appearance of the material is polyhedral particle-shaped and covered by fluffy substances. The material has the morphological characteristics that the specific surface area and the pore channel structure of the material are increased, and compared with the long strip structure of the material N-C-Al-900 in CN 108281679A, the material is more beneficial to the oxygen reduction reaction.

In another exemplary embodiment of the present disclosure, there is provided a use of the above-described nifro-doped carbon nanomaterial in the preparation of a fuel cell cathode catalyst.

In yet another exemplary embodiment of the present disclosure, a fuel cell is provided, the above-mentioned nitrogen-iron doped carbon nanomaterial as a fuel cell cathode catalyst.

Further, the fuel cell is a methanol fuel cell.

In yet another exemplary embodiment of the present disclosure, there is provided a use of the above-described nife-doped carbon nanomaterial in electrocatalysis.

In order to make the technical solutions of the present disclosure more clearly understood by those skilled in the art, the technical solutions of the present disclosure will be described in detail below with reference to specific embodiments.

Example 1

A preparation method of a nitrogen-iron doped carbon nano material comprises the following steps:

1) preparing a nano-scale metallic iron-organic framework material precursor: 1.3838mmol of 2-amino-1, 4-terephthalic acid is weighed, 1.3838mmol of ferric chloride hexahydrate is weighed and dissolved in 30mL of N, N-dimethylformamide, stirred until the ferric chloride hexahydrate is fully dissolved, then the mixture is added into a polytetrafluoroethylene reaction kettle, the reaction kettle is sealed, the mixture reacts for 20 hours at the temperature of 120 ℃, then the mixture is cooled to the room temperature, the reaction solution is filtered, the precipitate is washed for three times by the N, N-dimethylformamide, and then the mixture is placed into a vacuum drying oven to be dried for 12 hours, so that a brownish black powder product is obtained.

2) Preparing a nitrogen-iron doped carbon nano material (N-C-Fe): putting the nano-scale metallic iron-organic framework material precursor prepared in the step 1) into a tube furnace, and heating at 3 ℃ for min under the argon atmosphere^-1The temperature is raised to 600 ℃, the nitrogen-iron doped carbon nano material is prepared by roasting for 3 hours, and then the obtained material is treated by 2M hydrochloric acid, and the name of the obtained material is N-C-Fe-600.

Example 2

This example corresponds to example 1The difference is that the example is carried out at 3 ℃ min under argon atmosphere^-1The temperature is raised to 550 ℃, the nitrogen-iron doped carbon nano material is prepared by roasting for 3 hours, and then the obtained material is treated by 2M hydrochloric acid, and the name of the obtained material is N-C-Fe-550.

Example 3

This example is the same as example 1 except that it was conducted at 3 deg.C.min under an argon atmosphere^-1The temperature is raised to 650 ℃, the nitrogen-iron doped carbon nano material is prepared by roasting for 3 hours, and then the obtained material is treated by 2M hydrochloric acid, and the name of the obtained material is N-C-Fe-650.

Example 4

This example is the same as example 1 except that it was conducted at 3 deg.C.min under an argon atmosphere^-1The temperature is raised to 700 ℃, the nitrogen-iron doped carbon nano material is prepared by roasting for 3 hours, and then the obtained material is treated by 2M hydrochloric acid, and the name of the obtained material is N-C-Fe-700.

Example 5

This example is the same as example 1 except that it was conducted at 3 deg.C.min under an argon atmosphere^-1The temperature is raised to 800 ℃, the nitrogen-iron doped carbon nano material is prepared by roasting for 3 hours, and then the obtained material is treated by 2M hydrochloric acid, and the name of the obtained material is N-C-Fe-800.

Example 6

This example is the same as example 1 except that it was conducted at 3 deg.C.min under an argon atmosphere^-1The temperature is raised to 500 ℃, the nitrogen-iron doped carbon nano material is prepared by roasting for 3 hours, and then the obtained material is treated by 2M hydrochloric acid, and the name of the obtained material is N-C-Fe-500.

Example 7

An electrocatalytic oxygen reduction test comprising the steps of:

1) a glassy carbon electrode (diameter 3mm) was treated as follows: firstly, 0.3 mu m of alumina powder is used for grinding and polishing to obtain a mirror-surface smooth surface, then absolute ethyl alcohol and deionized water are used for ultrasonic washing in sequence, and then nitrogen is used for blow-drying for later use.

2) The working electrode was prepared as follows: dispersing 1mg of the synthesized N-C-Fe sample in 50 mu L of Nafion aqueous solution with the mass fraction of 0.5%, 300 mu L of ethanol and 300 mu L of deionized water, dispersing the material uniformly by ultrasonic, transferring about 8 mu L of the dispersed material to the surface of the treated glassy carbon electrode, and airing the glassy carbon electrode at room temperature to be detected; rotating a disc electrode (diameter 5mm) in the same way, transferring 20 mu L of the drop on the electrode surface, and placing and airing the drop at room temperature to be detected.

3) The three-electron system test was performed with an electrochemical workstation (CHI), which used a platinum wire as the counter electrode, a silver/silver chloride (saturated potassium chloride) electrode as the reference electrode, and a glassy carbon electrode decorated with a catalyst as the working electrode. 0.1 mol. L at saturation with oxygen^-1The electrocatalytic oxygen reduction test is carried out in the KOH solution, and oxygen is continuously introduced in the linear scanning test and the stability test.

Test results and discussion in example 1

1. Structural characterization of N-C-Fe-600

FIG. 1a and FIG. 1b are scanning electron microscope images of N-C-Fe-600 before and after carbonization, respectively, and it can be seen from the images that the morphology of the material is obviously changed after high temperature treatment at 600 ℃, and the edge of the material has obvious carbonization traces compared with the original morphology. In FIG. 1a, polyhedral particles having an average diameter of about 200nm and a length of about 250nm can be clearly observed. Subsequently, it was carbonized in Ar at 600 ℃ for 4 hours to convert into N-C-Fe. The surface of the polyhedron becomes rough and is covered by fluffy substances, and the specific surface area and pore channels of the material are increased by the morphological characteristics of the material; FIG. 1C and FIG. 1d are transmission electron microscope images of N-C-Fe-600 before and after carbonization of N-C-Fe-600, respectively, and it can be seen that the carbonized material has a certain degree of collapse due to high temperature, but the whole skeleton and morphology of the carbonized material still exist, and the channels are favorable for the oxygen reduction reaction.

FIG. 2a is the precursor (NH)₂XRD of MIL-88(Fe)), FIG. 2b is the XRD pattern of N-C-Fe-600, from FIG. 2a with standard NH₂Comparison of diffraction peaks of-MIL-88 (Fe), it can be seen that the material has been used to synthesize NH successfully₂MIL-88(Fe), a precursor of N-C-Fe-600. From FIG. 2b it can be seen that carbonized MOF mainly contains amorphous carbon, Fe₃C. Three species of Fe. Present at 2 theta angles of 23 deg. and 44 deg.Two broad peaks indicate that the product is mainly composed of amorphous carbon with disordered structure, and the two broad peaks respectively correspond to two diffraction peaks of graphite. Fe is formed in the carbonized material₃C and well corresponds to Fe₃Diffraction peak of C. The carbonized material also has corresponding diffraction peaks of Fe. The formation of such graphitized carbon plays an important role in the good electrical conductivity of the material.

FIG. 3a is an XPS energy spectrum of N-C-Fe-600, and the presence of carbon, nitrogen, oxygen, and iron elements demonstrates the successful synthesis of nitrogen and iron doped carbon materials. FIG. 3b shows the high resolution XPS spectrum of C1s in XPS with N-C-Fe-600, with peaks at 284.8eV, 286.9eV and 288.9eV corresponding to the bond C C, C-O, C-N. The presence of a C-N bond also further indicates the successful doping of N into the product. FIG. 3C shows the high resolution XPS spectrum of N1s in XPS with N-C-Fe-600, with the three peaks corresponding to pyridine nitrogen (N1 s: 398.53eV), pyrrole nitrogen (N1 s: 400.15eV), and graphite nitrogen (N1 s: 401.02eV), respectively. FIG. 3d is a high resolution XPS spectrum of Fe2p in XPS of N-C-Fe-600, with peaks at 710.7eV and 724.3eV corresponding to Fe2p3/2 and Fe2p1/2, respectively. Indicating the presence of Fe and Fe in the material₃C。

FIG. 4 is a Raman spectrum of N-C-Fe-600, which is a widely used tool for characterizing the detailed structural features of carbon-based materials in order to more closely describe the carbon in the material. The spectrum shows two major peaks, each due to 1360cm^-11590cm at D-band peak and missing graphite material^-1The G-band peak at (FIG. 3 a). I is_D/I_GThe ratio of (A) can indicate that the level of graphitization (degree of disorder and degree of defects) of the carbon within the N-C-Fe-600 material is very significant and that the edge planes are not ordered. The defect structure can provide an ORR active site, and is beneficial to the conduction of electrons in the material and the progress of an ORR reaction in an electrocatalytic process.

FIG. 5 is a graph showing the specific surface area of N-C-Fe-600 under 77K nitrogen, which is 136.309 cc/g. As can be seen from the figure, the adsorption/desorption isotherm of the carbonized material indicates that the material has a mesoporous structure. The inset in fig. 5 is a plot of the pore size distribution of the carbon material, and it can be seen from the inset that the product has a relatively uniform pore distribution with a pore size of about 19 nm. The porous structure of the carbon material greatly improves the specific surface area of the material, and has important significance for improving the activity of the electrochemical process and the mass transfer and diffusion of electrolyte on the surface of the catalyst.

FIG. 6 is the N-C-Fe-600 precursor (NH)₂-MIL-88), which is an effective method for analyzing the thermal stability of a material. There were two significant weight losses before 600 ℃, which was a loss of water and ligand in the material, and the weight of the material continued to decrease after 600 ℃, indicating that the structure of the material had collapsed significantly as the temperature increased. Therefore, 600 degrees is the most suitable carbonization temperature.

2. Characterization of electrochemical Properties of N-C-Fe

FIG. 7 shows the catalyst materials (NH) obtained at different carbonization temperatures₂MIL-88, N-C-Fe-500 in example 6, N-C-Fe-600 in example 1, N-C-Fe-700 in example 4, N-C-Fe-800 in example 5), 0.1 mol. L.L.saturated in oxygen^-1Linear sweep profile (LSV) in KOH solution. A Rotating Disk Electrode (RDE) was used during the test, and the rotation speed of fig. 7 was 1600 rpm. As can be seen from the figure, N-C-Fe-600 has a better initial potential (-0.15V) and a larger current density (5.1mA cm) than other materials^-2)。

FIG. 8a is a cyclic voltammogram of the N-C-Fe-600 catalyst material, from which it can be seen that under the condition of oxygen saturation, a distinct characteristic peak of oxygen reduction reaction appears, indicating that the material has distinct electrocatalytic activity for oxygen reduction reaction, and the potential of the reduction peak is-0.28V. FIG. 8b is 0.1 mol. L of N-C-Fe-600 modified electrode saturated with oxygen^-1Linear scanning curve and ring disk electrode test curve in KOH solution, the rotating speed is 1600rpm, and the scanning speed is 5mV^-1. The electron transfer number (n) of the catalyst during oxygen reduction was calculated using the following formula:

n＝4I_d/(I_d+I_r)/N (1)

I_dthe magnitude of the disk current during the test (5.10 mA/cm)²)，I_rThe magnitude of the loop current during the test (0.012 mA/cm)²) N is the collection coefficient of Pt ring(0.43)。

It is found by calculation that the electron transfer number of the catalyst in the oxygen reduction process is close to the ideal four-electron transfer n of 3.7.

Also, in order to explore the reaction mechanism of the reaction, the present disclosure further studied the kinetics of the electrocatalytic oxygen reduction reaction of N-C-Fe-600 using rotating disk voltammetry. Its polarization curve is 0.1 mol.L at oxygen saturation^-1FIG. 8c, which shows that the limiting diffusion current density increases with increasing rotation speed in the voltage range of-0.8 to 0V in the KOH solution. FIG. 8d is the corresponding Koutecky-Levich (K-L) curve, which shows that the linear relationship is good, and this shows that N-C-Fe-600 has similar electron transfer number and the oxygen reduction reaction conforms to the first order reaction kinetics under different voltages. The number of electron transfers (n) and the kinetic limiting current density of the oxygen reduction reaction are calculated by RDE and on the basis of the K-L equation:

1/J＝1/J_L+1/J_K＝1/Bω^0.5+1/J_K (2)

B＝0.62nFC_O(D_O)^2/3v^-1/6 (3)

J_K＝nFkC_O (4)

wherein J is the current density obtained in the test, J_KIs the kinetic limiting current density, J_LIs a diffusion limiting current density, [ omega ] is a rotational angular velocity of the motor, n is a total number of electron transfers in the oxygen reduction reaction, and F is a Faraday constant (96485℃ mol.)^-1)。C_OIs the volume concentration of oxygen, D_OIs the diffusion coefficient of oxygen in the KOH electrolyte, v is the dynamic viscosity of the electrolyte, and k is the electron transfer rate constant. And at 0.1 mol. L^-1In KOH solution, C_O＝1.2×10^-6mol·cm^-3，D_O＝1.9×10^-5cm²·s^-1，v＝1.0×10^-2cm²·s^-1. According to the above formula, N can be obtained by calculating the slope of the K-L curve to obtain an electron transfer number of 3.7 for N-C-Fe-600, while N-C-Al-90 is the material in CN 108281679AThe electron transfer number of 0 is 3.3, and the result shows that the catalytic process of the N-C-Fe-600 material is closer to the four-electron transfer reaction. The performance is improved by the feature and the porous structure of the material in the form of polyhedral particles, and by doping the porous carbon material with non-metallic iron, active sites are increased, and the catalytic performance is improved.

The stability and methanol resistance of the material are also main indexes for measuring the practical application of the catalyst in the fuel cell. The disclosure is at 0.1 mol.L of oxygen saturation^-1The stability and methanol resistance of the N-C-Fe-600 catalyst was tested in KOH solution. As can be seen in FIG. 9a, after 30000s of operation, the N-C-Fe-600 catalyst material loss is significantly less than commercial Pt/C, with better stability. In FIG. 9b, the N-C-Fe-600 catalyst material showed only a small change in magnitude after 1M methanol addition, while the commercial Pt/C showed a large change in current, indicating that the methanol resistance of the N-C-Fe-600 catalyst is significantly better than that of the Pt/C. These results indicate that this material has great potential application value in direct methanol fuel cells. Compared with N-C-Al-900 which is the material in CN 108281679A, the obtained catalyst has better catalytic performance, is closer to the ideal four-electron transfer reaction, and also has better methanol resistance and stability.

The above embodiments are preferred embodiments of the present disclosure, but the embodiments of the present disclosure are not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present disclosure should be regarded as equivalent replacements within the scope of the present disclosure.

Claims

1. A preparation method of a fuel cell cathode catalyst is characterized by comprising the following steps:

taking 2-amino-terephthalic acid and ferric salt as raw materials, preparing a metallic iron-organic framework material by a solvothermal synthesis method, putting the metallic iron-organic framework material in N, N-dimethylformamide for washing, filtering, drying a filtered precipitate to obtain a precursor, roasting the precursor at 550-650 ℃ in an inert gas atmosphere,then acid treatment is carried out to obtain the N-Fe doped carbon nano material, and the N-Fe doped carbon nano material comprises amorphous carbon and Fe₃C. Three species of Fe;

wherein, the solvent adopted in the solvothermal synthesis method is an N, N-dimethylformamide organic solvent.

2. The method of claim 1, wherein: the molar ratio of the 2-amino-terephthalic acid to the iron salt is 1: 1.

3. The method of claim 1, wherein: the adding ratio of the 2-amino-terephthalic acid to the N, N-dimethylformamide is 1-2 mmol: 25-35 mL.

4. The method of claim 1, wherein: 1.3838mmol of 2-amino-terephthalic acid and 1.3838mmol of iron salt are dissolved in 30mL of N, N-dimethylformamide solution and reacted by a solvothermal synthesis method.

5. The method of claim 1, wherein: the temperature of solvothermal synthesis is 110-130 ℃, and the synthesis time is 19-21 h.

6. The method of claim 1, wherein: the inert gas is argon.

7. The method of claim 1, wherein: the temperature rise rate of the roasting is 2-4 ℃ per minute^-1。

8. The method of claim 7, wherein: the temperature rise rate of the roasting is 3 ℃ per minute^-1。

9. The method of claim 1, wherein: the roasting time is 3-4 h.

10. The method of claim 1, wherein: the drying is vacuum drying, and the drying time is 11-13 h.

11. The method of claim 1, wherein: the acid used for the acid treatment is hydrochloric acid.

12. The method of claim 11, wherein: the concentration of hydrochloric acid was 2M.

13. The method of claim 1, wherein: the roasting temperature is 595-605 ℃.

14. The method of claim 13, wherein: the roasting temperature is 600 ℃.

15. The nitrogen-iron doped carbon nanomaterial prepared by the method of any one of claims 1-14.

16. Use of the nitrogen-iron doped carbon nanomaterial of claim 15 in the preparation of a fuel cell cathode catalyst.

17. A fuel cell, characterized by: the use of the ferronitrogen-doped carbon nanomaterial of claim 15.

18. Use of the nifc-doped carbon nanomaterial of claim 15 in electrocatalysis.