CN113889628A - Preparation and application of Fe-N-CNFs catalyst based on Fe-MIL - Google Patents

Preparation and application of Fe-N-CNFs catalyst based on Fe-MIL Download PDF

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CN113889628A
CN113889628A CN202111156018.7A CN202111156018A CN113889628A CN 113889628 A CN113889628 A CN 113889628A CN 202111156018 A CN202111156018 A CN 202111156018A CN 113889628 A CN113889628 A CN 113889628A
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catalyst
mil
cnfs
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侯明
罗文哲
邵志刚
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Dalian Institute of Chemical Physics of CAS
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01M4/8605—Porous electrodes
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    • H—ELECTRICITY
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    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8636—Inert electrodes with catalytic activity, e.g. for fuel cells with a gradient in another property than porosity
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    • H01M2004/8678—Inert electrodes with catalytic activity, e.g. for fuel cells characterised by the polarity
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Abstract

The invention provides a preparation method and application of Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL, wherein the method comprises the steps of firstly reacting ferric chloride hexahydrate and terephthalic acid in N, N-dimethylformamide to generate an Fe-MIL precursor, then mixing the Fe-MIL precursor and a nitrogen-containing binder in the N, N-dimethylformamide to carry out electrostatic spinning to prepare nano-fibers, and carrying out presintering pyrolysis to prepare the Fe-N-CNFs (carbon nanofibers) catalyst. The catalyst has the advantages of large active area, strong electron transfer capability and strong mass transfer capability, so that the catalyst has strong capability of catalyzing oxygen reduction reaction. In addition, the synthetic material has low price, and the cost of the catalyst can be reduced, so the catalyst has a wide application prospect in the aspect of proton exchange membrane fuel cells.

Description

Preparation and application of Fe-N-CNFs catalyst based on Fe-MIL
Technical Field
The invention belongs to the field of fuel cells, and particularly relates to a preparation method of a Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL and application of the Fe-N-CNFs catalyst in oxygen reduction reaction of a fuel cell.
Background
With the worsening of energy and environmental problems and the increasing demand for clean energy, proton exchange membrane fuel has received much attention due to the advantages of high energy conversion efficiency, high power density, zero pollutant emission, and the like. However, the use of high-priced Pt/C catalyst for the cathode thereof has hindered the large-scale application of the proton exchange membrane fuel cell. Therefore, the development of a non-noble metal catalyst with low price and high activity is an urgent matter, and the Fe-N-C catalyst has made great progress as the non-noble metal catalyst which is most likely to replace the Pt/C catalyst, wherein the iron-nitrogen carbon nanofiber catalyst has excellent performance (J.L.Shui, C.Chen, et al.PNAS, 2015, 112(34), 10629-10634).
The iron-nitrogen-carbon nanofiber catalyst is widely researched as a cathode oxygen reduction catalyst of a proton exchange membrane fuel cell because of high graphitization degree, high specific surface area and a layered microporous structure. In the prior art, Fe precursors, conventional carbon materials (such as activated carbon) and other raw materials are usually mixed and then directly pyrolyzed to obtain the Fe-N-C catalyst, and the Fe-N-C catalyst prepared by the method has the problems of low Fe content, small porosity, low specific surface area and the like, so that the number of active sites of the catalyst is low, and the mass transport capacity and the electron conduction capacity are limited.
Disclosure of Invention
Aiming at the problems of small porosity, poor conductivity, low specific surface area and the like of the Fe-N-C catalyst prepared by the existing method, the Fe-MIL is taken as an Fe source (the Fe-MIL is one of metal organic framework materials), the Fe-N-CNFs catalyst is prepared by adopting the electrostatic spinning technology, and the Fe-N-CNFs catalyst is applied to a proton exchange membrane fuel cell, so that the activity, the mass transfer capacity and the conductivity of a catalyst layer are improved.
The technical scheme of the invention is as follows:
a preparation method of Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL comprises the following steps:
(1) dissolving Fe-MIL in a solvent 1, adding an electrostatic spinning nitrogen-containing binder, and stirring at 10-24 ℃ for 12-24 hours to prepare a mixed solution;
(2) carrying out electrostatic spinning on the mixed solution to prepare nano fibers;
(3) the nano-fiber is firstly presintered at 200-300 ℃ for 2-5h and then pyrolyzed at 700-1000 ℃ for 2-5h to prepare the Fe-N-CNFs (carbon nanofibers) catalyst.
In the step (1): the mass ratio of the Fe-MIL to the electrostatic spinning nitrogen-containing binder is 1-2.5: 1; the mass fraction of the electrostatic spinning nitrogen-containing binder in the mixed solution is 10-16%. The nitrogen content of the electrostatic spinning nitrogen-containing binder is not less than 12.61 wt%.
As a preferable technical scheme, the solvent 1 is N, N-dimethylformamide.
Preferably, the nitrogen-containing binder for electrostatic spinning is Polyacrylonitrile (PAN) or polyvinylpyrrolidone (PVP). The mass fraction of Fe in the Fe-MIL is 20-30%.
As a preferred technical scheme, the dissolving process in the step (1) is that Fe-MIL is added into a solvent 1, ultrasonic treatment is carried out for 20-30min, and then an electrostatic spinning nitrogen-containing binder is added.
As a preferred technical scheme, in the step (2), the voltage of electrostatic spinning is 15-30kV, the liquid inlet flow is 0.4-0.6ml/h, and the spinning time is 4-10 h.
As a preferred technical scheme, the pre-burning process of the step (3) is carried out under the air condition, and the pyrolysis process is carried out under the argon gas condition.
As a preferred technical scheme, the Fe-MIL is prepared by the following steps:
(a) ultrasonically dissolving ferric chloride hexahydrate and terephthalic acid in a solvent 2 to prepare a mixed solution A;
(b) reacting the mixed solution A at the temperature of 140-160 ℃ for 12-24h, preferably at the temperature of 150 ℃ for 12h, centrifuging, washing and drying to obtain Fe-MIL;
the molar ratio of the ferric chloride hexahydrate to the terephthalic acid is 1: 1; the solvent 2 is N, N-dimethylformamide.
As a preferred technical scheme, in the step (a), the ultrasonic time is 5-10 minutes; the drying temperature in the step (b) is 80 ℃, and the drying time is 6-12 h.
The invention also provides Fe-N-CNFs (carbon nanofibers) catalysts based on Fe-MIL prepared by any one of the methods.
As a preferred technical scheme, the average pore radius of the catalyst is 3.0-4.0nmThe specific surface area is 330-410m2The mass fraction of Fe in the catalyst is 30-40%, and the Fe content is increased compared to Fe-MIL, because pyrolysis causes carbon loss in Fe-MIL precursor, so that the Fe content is increased after pyrolysis.
The invention also provides the application of the Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL in fuel cells as a cathode catalyst.
Advantageous effects
(1) The Fe-MIL precursor is used as the Fe source, so that compared with other Fe sources, the Fe content in the catalyst can be increased, and the particle curl generated by Fe in pyrolysis is reduced; large amounts of Fe in Fe-MIL precursors can be used to form Fe-N4The active sites further improve the catalytic activity of the catalyst, so that the Fe-N-CNFs catalyst based on Fe-MIL has more active sites, high conductivity and higher mass conversion efficiency. The material is applied to the cathode oxygen reduction reaction of a proton exchange membrane fuel cell: the catalyst has high activity, large specific surface area, high mass transmission capability and good electron transmission capability, and the oxygen reduction catalytic performance of the catalyst is improved.
(2) According to the invention, the nitrogen-containing binder used in electrostatic spinning is simultaneously used as a nitrogen source, so that the use of nitrogen-containing organic matters can be omitted, the Fe content of the catalyst is improved, and meanwhile, the nanofiber catalyst obtained by the electrostatic spinning method is used for replacing a conventional carbon material as a carrier, so that the mass transport capacity, the electron conduction capacity and the number of active sites can be improved; meanwhile, the porosity of the catalyst can be improved, the contact between active sites and reactants can be improved, and the catalytic activity of the catalyst is further improved.
(3) The mixing temperature of the Fe-MIL precursor and the nitrogen-containing binder in the solvent is 10-24 ℃, the temperature is higher than the temperature, liquid drops can appear during spinning, a needle can be blocked when the temperature is lower than the temperature, the nitrogen content of the nitrogen-containing binder is not lower than 12.61 wt%, the nitrogen content in the nanofiber formed by electrostatic spinning is not high when the nitrogen content is lower than the temperature, the active sites of the catalyst Fe-N4 synthesized by pyrolysis are few, and the performance of the catalyst is not high.
(4) The method takes polyacrylonitrile as a nitrogen source and Fe-MIL as an iron source, has low price and simple reaction conditions, and can be widely applied.
Drawings
FIG. 1 is an SEM image of the Fe-MIL precursor prepared in example 1.
FIG. 2 is an SEM image of Fe-MIL precursor electrospun nanofibers prepared in example 1.
FIG. 3 is an SEM photograph of Fe-N-CNFs (carbon nanofibers) based on Fe-MIL prepared in example 1.
FIG. 4 is an oxygen reduction polarization curve obtained by a Rotating Disk Electrode (RDE) test in a 0.1MKOH solution for Fe-N-CNFs (carbon nanofibers) based on Fe-MIL prepared in example 1, example 2, example 3 and example 4.
FIG. 5 is an XRD pattern of Fe-N-CNFs (carbon nanofibers) based Fe-MIL catalyst prepared in example 2.
FIG. 6 is a Raman diagram of Fe-N-CNFs (carbon nanofibrers) based Fe-MIL catalyst prepared in example 2.
FIG. 7 is an XPS spectrum of the N element of the Fe-N-CNFs (carbon nanofibers) based Fe-MIL catalyst prepared in example 2.
FIG. 8 is an XPS spectrum of Fe element of Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL prepared in example 2.
FIG. 9 is a nitrogen adsorption and desorption curve of Fe-N-CNFs (carbon nanofibers) based on Fe-MIL prepared in example 2.
FIG. 10 is a graph showing the pore size distribution of Fe-N-CNFs (carbon nanofibers) based Fe-MIL catalyst prepared in example 2.
FIG. 11 is an oxygen reduction polarization curve obtained in 0.1M KOH solution by Rotating Disk Electrode (RDE) testing of Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL prepared in example 2, comparative example 1, comparative example 2, and catalyst prepared in comparative example 3 with a commercial 20% Pt/C catalyst.
FIG. 12 is a methanol resistance test of Fe-N-CNFs (carbon nanofibres) catalyst based on Fe-MIL prepared in example 2 with a commercial 20% Pt/C catalyst.
FIG. 13 is a graph showing the change in current during the constant voltage decay of Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL prepared in example 2 and a commercial 20% Pt/C catalyst.
FIG. 14 is an oxygen reduction polarization curve of Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL prepared in example 2 and a commercial 20% Pt/C catalyst obtained by a Rotating Ring Disk Electrode (RRDE) test.
FIG. 15 is a plot of cell polarization curves and power density for Fe-N-CNFs (carbon nanofibers) based on Fe-MIL catalyst prepared in example 2 as cathode catalyst.
FIG. 16 is an XRD pattern of Fe-N-CNFs (carbon nanofibers) based Fe-MIL catalyst prepared in example 3.
FIG. 17 is a Raman diagram of Fe-N-CNFs (carbon nanofibrers) based Fe-MIL catalyst prepared in example 3.
FIG. 18 is an XPS spectrum of the N element of Fe-N-CNFs (carbon nanofibers) based on Fe-MIL prepared in example 4.
FIG. 19 is an XPS spectrum of Fe element of Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL prepared in example 4.
FIG. 20 is a nitrogen adsorption and desorption curve of Fe-N-CNFs (carbon nanofibers) based on Fe-MIL prepared in example 4.
FIG. 21 is a graph showing the pore size distribution of Fe-N-CNFs (carbon nanofibers) based Fe-MIL catalyst prepared in example 4.
Fig. 22 is an SEM image of the catalyst prepared in comparative example 3.
FIG. 23 is an oxygen reduction polarization curve obtained by Rotating Disk Electrode (RDE) testing in 0.1MKOH solution for Fe-N-CNFs (carbon nanofibers) based on Fe-MIL prepared in example 3, example 5, example 6 and example 7.
FIG. 24 is a nitrogen adsorption and desorption curve for the catalyst prepared in comparative example 3 based on MIL-NC-1.5-800.
FIG. 25 is an oxygen reduction polarization curve obtained by a Rotating Disk Electrode (RDE) test in a 0.1M KOH solution for Fe-N-CNFs (carbon nanofibers) based on Fe-MIL prepared in comparative example 4 and example 2.
FIG. 26 is an oxygen reduction polarization curve obtained by Rotating Disk Electrode (RDE) testing of catalysts prepared in comparative example 5 and example 2 in 0.1M KOH.
FIG. 27 shows that catalysts prepared in comparative example 6 and example 2 were tested by Rotating Disk Electrode (RDE) at 0.1M HClO4And (4) obtaining an oxygen reduction polarization curve of the solution.
Detailed Description
A process for the preparation of Fe-N-CNFs (carbon nanofibers) catalysts based on Fe-MIL, comprising the following steps:
(1) ultrasonically dissolving ferric chloride hexahydrate and terephthalic acid in N, N-dimethylformamide, wherein the molar ratio of the ferric chloride hexahydrate to the terephthalic acid is 1: 1, and the ultrasonic time is 5-10 minutes;
(2) reacting the mixed solution at 150 ℃ for 12h, centrifuging, filtering, washing, and drying at 80 ℃ for 6-12h to obtain a precursor Fe-MIL;
(3) adding a precursor Fe-MIL into N, N-dimethylformamide, performing ultrasonic treatment for 20-30min, adding Polyacrylonitrile (PAN) or polyvinylpyrrolidone (PVP), and stirring at room temperature for 12-24h to obtain a mixed solution, wherein the mass ratio of the precursor Fe-MIL to the Polyacrylonitrile (PAN) or polyvinylpyrrolidone (PVP) is 1-2.5: 1, and the mass fraction of the Polyacrylonitrile (PAN) or polyvinylpyrrolidone (PVP) is 10-16%;
(4) carrying out electrostatic spinning on the mixed solution for 4-10h under the conditions that the voltage is 15-30kV and the liquid inlet flow is 0.4-0.6ml/h to obtain nano fibers;
(5) the nano-fiber is firstly presintered for 2-5h at 200-300 ℃ under the air atmosphere, and then pyrolyzed for 2-5h at 1000 ℃ under 700-1000 ℃ under the argon atmosphere to prepare the Fe-N-CNFs (carbon nanofibers) catalyst.
Example 1
A process for the preparation of Fe-N-CNFs (carbon nanofibers) catalysts based on Fe-MIL, comprising the following steps:
(1) dissolving 1.084g of ferric chloride hexahydrate and 0.664g of terephthalic acid in 197ml of N, N-dimethylformamide, and ultrasonically dispersing for 5min to prepare a mixed solution;
(2) and stirring the mixed solution at the constant temperature of 150 ℃ for reaction for 12h, centrifuging and washing after the reaction is finished, and drying at the temperature of 80 ℃ for 6h to obtain a brown Fe-MIL precursor.
(3) Adding 0.5g of precursor Fe-MIL into 5ml of N, N-dimethylformamide, carrying out ultrasonic treatment for 30min, adding 0.5g of Polyacrylonitrile (PAN), and stirring at 20 ℃ for 24h to obtain a mixed solution;
(4) carrying out electrostatic spinning on the mixed solution for 5 hours under the voltage of 25kV and the liquid inlet flow of 0.5ml/h to obtain nano fibers;
(5) the nano-fiber is firstly presintered for 2h at the temperature rising speed of 5 ℃/min to 250 ℃ in the air atmosphere, and then is pyrolyzed for 2h at the temperature rising speed of 5 min/DEG C to 800 ℃ in the argon atmosphere, thus obtaining the Fe-N-CNFs (carbon nanofibers) catalyst.
Fig. 1 shows that the Fe-MIL precursor is a biconical hexagonal prism.
FIG. 2 shows that the Fe-MIL precursor nanofibers are very uniform with radii between 100-200 nm.
FIG. 3 shows that the nanofiber catalyst radius is also between 100 and 200 nm.
FIG. 4 is an oxygen reduction polarization curve of Fe-N-CNFs catalysts prepared in examples 1-4, measured by a Rotating Disk Electrode (RDE), and it can be seen that the half-wave potential of the synthesized catalyst of example 2 is the largest, higher than those of examples 1, 3 and 4, indicating that the optimum amount of Fe-MIL added is 0.75g, i.e., Fe-MIL: the optimal mass ratio of PAN is 1.5: 1.
Example 2
This example of a method for preparing Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL referring to example 1, except that the Fe-MIL precursor added in step (3) was 0.75g, and the mass ratio of the Fe-MIL precursor to Polyacrylonitrile (PAN) was 1.5: 1.
FIG. 5 shows that the catalyst contains Fe and Fe3C crystal, nitrogen-doped carbon nanofiber-coated Fe and Fe3The C particles may act as active sites for the catalyst.
FIG. 6 shows that the degree of graphitization of the catalyst is higher, IG/IDThe high graphitization degree can improve the conductive electron capability of the catalyst, and further improve the catalytic activity of the catalyst, namely 1.06.
Fig. 7 shows that the active components of the catalyst, graphite nitrogen and pyridine nitrogen, account for 48.7% of the total, the graphite nitrogen can increase the limiting current density, and the pyridine nitrogen can improve the initial potential.
FIG. 8 shows that the catalyst containsWith Fe-N2P1/2，Fe(III)2P1/2、Fe(III)2P3/2、Fe-N 2P3/2、Fe 2P3/2And the successful doping of Fe into the structure of the carbon nanofiber is demonstrated to form Fe-N active sites.
FIG. 9 shows that the catalyst has a pore specific surface area of 401.97m2In terms of the specific surface area, the average pore diameter is 3.932, the mass transfer capacity of the catalyst can be improved due to the large specific surface area, and the layered structure of micropores, mesopores and macropores shortens the mass transfer distance between reactants and active sites and improves the active site density of the catalyst.
FIG. 11 shows that the half-wave potential of the Fe-N-CNFs (carbon nanofibers) catalyst prepared in example 2 is close to that of commercial Pt/C by about 50mV, but is much higher than that of the catalysts synthesized in comparative example 1, comparative example 2 and comparative example 3, indicating that the catalysts synthesized by electrospinning have higher activity.
FIG. 12 shows that the Fe-N-CNFs (carbon nanofibers) catalyst is hardly affected by methanol relative to the Pt/C catalyst, indicating that the synthesized catalyst has strong methanol resistance.
FIG. 13 shows that under the condition of constant voltage decay, the current of the Pt/C catalyst decays by 30.61%, while the current of the Fe-N-CNFs (carbon nanofibers) catalyst only decays by 13.78%, which indicates that the catalyst has strong anti-decay capability.
FIG. 14 shows that the half-wave potential of the loop current of the Pt/C catalyst is slightly higher than that of the Fe-N-CNFs (carbon nanofibers) catalyst, which indicates that the catalyst has H2O2The yield will be slightly higher, but not very high, mainly proceeding with the ORR reaction in the 4-electron reaction pathway.
FIG. 15 shows that the highest power density of the PEM fuel cell using Fe-N-CNFs (carbon nanofibers) as the cathode catalyst can reach 167.34mW/cm2The synthesized catalyst has better performance.
Example 3
This example of a method for preparing Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL referring to example 1, except that the Fe-MIL precursor added in step (3) was 1.0g, and the mass ratio of the Fe-MIL precursor to Polyacrylonitrile (PAN) was 2: 1.
FIG. 16 shows that the catalyst contains Fe and Fe3C crystal, nitrogen-doped carbon nanofiber-coated Fe and Fe3The C particles can act as active sites of the catalyst, as in example 2.
FIG. 17 shows that the degree of graphitization of the catalyst is higher, IG/IDThe high graphitization degree can improve the electron conducting capability of the catalyst and further improve the catalytic activity of the catalyst, which is slightly higher than the graphitization degree of example 2.
Example 4
This example of a method for preparing Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL referring to example 1, except that the Fe-MIL precursor added in step (3) was 1.25g, and the mass ratio of the Fe-MIL precursor to Polyacrylonitrile (PAN) was 2.5: 1.
Fig. 18 shows that the active components of the catalyst, graphite nitrogen and pyridine nitrogen, account for 26.2% of the total, and are much lower than those of the catalyst synthesized in example 2, so that the performance is poorer than that of the catalyst synthesized in example 2.
FIG. 19 shows that the catalyst contains Fe (III)2P1/2、Fe(III)2P3/2、Fe-N 2P3/2、Fe 2P3/2And shows that Fe is successfully doped into the structure of the carbon nano fiber to form Fe-N active sites, which is basically consistent with example 2.
FIG. 20 shows that the catalyst has a pore specific surface area of 329.674m2In FIG. 21, it can be seen that the average pore diameter is 3.929, the specific surface area is lower than that of example 2, the average pore diameter is substantially the same, and the mass transfer capability of the catalyst synthesized in example 4 is slightly inferior.
Example 5
This example of a method for preparing Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL referring to example 1, except that the Fe-MIL precursor added in step (3) was 1.0g, the mass ratio of the Fe-MIL precursor to Polyacrylonitrile (PAN) was 2: 1, and the pyrolysis temperature in step (5) was 700 ℃.
FIG. 23 is an oxygen reduction polarization curve of Fe-N-CNFs catalysts prepared in examples 3, 5, 6 and 7, which was measured by a Rotating Disk Electrode (RDE), and the half-wave potential of the synthesized catalyst in example 3 was the largest and higher than those in examples 5-7, indicating that the optimal temperature for pyrolysis was 800 ℃.
Example 6
This example of a method for preparing Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL referring to example 1, except that the Fe-MIL precursor added in step (3) was 1.0g, the mass ratio of the Fe-MIL precursor to Polyacrylonitrile (PAN) was 2: 1, and the pyrolysis temperature in step (5) was 900 ℃.
Example 7
This example of a method for preparing Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL referring to example 1, except that the Fe-MIL precursor added in step (3) was 1.0g, the mass ratio of the Fe-MIL precursor to Polyacrylonitrile (PAN) was 2: 1, and the pyrolysis temperature in step (5) was 1000 ℃.
Comparative example 1
Comparative example 1 method for preparing N-CNFs (carbon nanofibers) catalyst reference was made to example 1, except that no Fe-MIL precursor was added in step (3).
Comparative example 2
Comparative example 2 method for preparing an Fe-MIL-800 based catalyst reference is made to example 1, except that the Fe-MIL precursor is pre-fired and then pyrolyzed without performing steps (3) (4).
Comparative example 3
Comparative example 3 method for preparing MIL-NC-1.5-800 catalyst reference example 1, except that Fe-MIL was mixed with polyacrylonitrile by grinding, not mixed in solution, and then spun.
It can be seen from fig. 22 that the catalyst synthesized in comparative example 3 has a blocky morphology, which is disadvantageous in mass transfer and active site exposure, and thus has poor performance.
FIG. 24 shows that the specific surface area of the pores of the catalyst synthesized in comparative example 3 is 291.039m2The activity of oxygen reduction is shown in figure 11, and the catalytic activity of comparative example 3 is lower than that of example 2, which shows that the nanofiber structure can increase the porosity, shorten the mass transfer distance between reactants and products, increase the number of active sites and further improve the catalytic activity.
Comparative example 4
This comparative example method for preparing Fe-N-CNFs (carbon nanofibers) catalyst based on Fe-MIL referring to example 1, except that the Fe-MIL precursor added in step (3) was 0.1g, the mass ratio of the Fe-MIL precursor to Polyacrylonitrile (PAN) was 1: 5, and the pyrolysis temperature in step (5) was 800 ℃.
FIG. 25 shows that the catalyst synthesized in comparative example 4 has much lower performance than example 2, indicating that the ratio of Fe-MIL to PAN is less than 1: 1, the performance of the synthesized catalyst is very poor, and when the ratio is higher than 2.5: 1, the viscosity of the slurry is too low to perform spinning.
Comparative example 5
This comparative example method for preparing Fe-CNFs (carbon nanofibers) catalyst based on Fe-MIL referring to example 1, except that the binder is polyethylene oxide (PEO) instead of Polyacrylonitrile (PAN).
Fig. 26 shows that the catalyst synthesized in comparative example 5 has much lower performance than that of example 2, and illustrates that the nitrogen content has a significant influence on the catalyst performance, the nitrogen content of PEO is 0 and Fe-MIL does not contain nitrogen, so that the catalyst synthesized by PEO as a binder has extremely poor performance, and the nitrogen content of the binder must be increased in order to improve the catalyst performance.
Comparative example 6
This comparative example method for preparing ZIF-8(Fe) -based Fe-N-cnfs (carbon nanofibers) catalysts referring to example 1, except that the precursor is ZIF-8(Fe) instead of Fe-MIL, the pyrolysis temperature is 1050 ℃, which is the optimal pyrolysis temperature for ZIF-8(Fe) -based precursors, wherein ZIF-8(Fe) is prepared as follows: 2.05g of 2-methylimidazole and 1.83g of butylamine dissolved in 200ml of anhydrous methanol, 2.97g of Zn (NO)3)2·6H2O and 0.2g FeCl2·4H2Dissolving O in 200ml of anhydrous methanol, mixing the two solutions, standing for 1 hour, centrifuging, washing and drying to obtain a ZIF-8(Fe) precursor.
FIG. 27 shows that the performance of the catalyst synthesized in comparative example 6 is lower than that of example 2, the Fe content in Fe-MIL is 20-30%, and the Fe content in ZIF-8(Fe) is lower than 5%, which indicates that the performance of the precursor spinning pyrolysis synthesis catalyst with high Fe content is better.

Claims (10)

1. The preparation method of the Fe-N-CNFs catalyst based on Fe-MIL is characterized by comprising the following steps: the method comprises the following steps:
(1) dissolving Fe-MIL in a solvent 1, adding an electrostatic spinning nitrogen-containing binder, and stirring at 10-24 ℃ for 12-24 hours to prepare a mixed solution;
(2) carrying out electrostatic spinning on the mixed solution to prepare nano fibers;
(3) pre-burning the nano-fiber at 200-300 ℃ for 2-5h, and then pyrolyzing the nano-fiber at 700-1000 ℃ for 2-5h to prepare the Fe-N-CNFs catalyst;
the mass ratio of the Fe-MIL to the electrostatic spinning nitrogen-containing binder is 1-2.5: 1; the mass fraction of the electrostatic spinning nitrogen-containing binder in the mixed solution is 10-16%; the nitrogen content of the electrostatic spinning nitrogen-containing binder is not less than 12.61 wt%.
2. The method for preparing Fe-N-CNFs catalyst based on Fe-MIL according to claim 1, wherein: the solvent 1 is N, N-dimethylformamide; the electrostatic spinning nitrogen-containing binder is Polyacrylonitrile (PAN) or polyvinylpyrrolidone (PVP); the mass fraction of Fe in the Fe-MIL is 20-30%.
3. The method for preparing Fe-N-CNFs catalyst based on Fe-MIL according to claim 1, wherein: in the step (1), Fe-MIL is added into the solvent 1, and nitrogen-containing electrostatic spinning binder is added after ultrasonic treatment for 20-30 min.
4. The method of preparing Fe-N-CNFs catalysts based on Fe-MIL as claimed in claim i, characterized in that: in the step (2), the voltage of electrostatic spinning is 15-30kV, the liquid inlet flow is 0.4-0.6ml/h, and the spinning time is 4-10 h.
5. The method for preparing Fe-N-CNFs catalyst based on Fe-MIL according to claim 1, wherein: and (4) performing the pre-burning process in the step (3) under the air condition, and performing the pyrolysis process under the argon condition.
6. The method for preparing Fe-N-CNFs catalyst based on Fe-MIL according to claim 1, wherein: the Fe-MIL is prepared by the following steps:
(a) ultrasonically dissolving ferric chloride hexahydrate and terephthalic acid in a solvent 2 to prepare a mixed solution A;
(b) reacting the mixed solution A at the temperature of 140-;
the molar ratio of the ferric chloride hexahydrate to the terephthalic acid is 1: 1; the solvent 2 is N, N-dimethylformamide.
7. The method for preparing Fe-N-CNFs catalysts based on Fe-MIL according to claim 6, wherein: in the step (a), the ultrasonic time is 5-10 minutes; the drying temperature in the step (b) is 80 ℃, and the drying time is 6-12 h.
8. An Fe-N-CNFs catalyst prepared by the process of any one of claims 1 to 7.
9. The catalyst of claim 8, wherein the catalyst has an average pore radius of 3.0 to 4.0 nm; the specific surface area is 330-410m2The mass fraction of Fe in the catalyst is 30-40%.
10. Use of the Fe-N-CNFs catalyst according to claim 8 as a cathode catalyst in fuel cells.
CN202111156018.7A 2021-11-15 2021-11-15 Preparation and application of Fe-N-CNFs catalyst based on Fe-MIL Pending CN113889628A (en)

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