CN112701307A

CN112701307A - Double MOF (metal organic framework) connection structure nano composite electrocatalyst for proton membrane fuel cell and preparation method thereof

Info

Publication number: CN112701307A
Application number: CN202110177711.6A
Authority: CN
Inventors: 肖高; 张梦瑶
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2021-02-09
Filing date: 2021-02-09
Publication date: 2021-04-23
Anticipated expiration: 2041-02-09
Also published as: CN112701307B

Abstract

The invention discloses a double MOF (metal organic framework) connection structure nano composite electrocatalyst for a proton membrane fuel cell, which is a catalyst made of double MOF nano materials, wherein the active substance of the nano materials is ZIF-8@ TA/ZIF-67@ TA. The problems of the existing fuel cell catalyst are solved, the defects of the prior art, the problems of single precursor obstacle and synthesis cost of the existing fuel cell catalyst are overcome, and the defects of high cost, toxicity and the like of a Pt-based catalytic material are overcome; based on the unique connection structure of ZIF-8 and ZIF-67, a metal organic framework nano composite material for a proton membrane fuel cell is developed, and the metal organic framework nano composite material has the advantages of high initial potential, half-slope potential, excellent limiting current, excellent stability, good methanol tolerance, strong methanol poisoning resistance and the like.

Description

Double MOF (metal organic framework) connection structure nano composite electrocatalyst for proton membrane fuel cell and preparation method thereof

Technical Field

The invention belongs to the technical field of proton membrane fuel cell catalysts, and particularly relates to a double MOF (metal organic framework) connection structure nano composite electrocatalyst for a proton membrane fuel cell and a preparation method thereof.

Background

The proton membrane fuel cell (PEMFC) has the characteristics of high specific energy, low-temperature quick start, convenient operation, high and stable operation, environmental protection and the like, is considered to be an ideal power source for replacing an internal combustion engine, is applied to the aspects of national defense, aerospace, communication, portable power supplies, new energy automobiles and the like, and is concerned by wide scholars. At present, the problems of overhigh cost, short service life and the like of the PEMFC still face, so that the PEMFC cannot be widely applied and further development of the PEMFC in the industrialization process is limited. In order to improve the performance of the PEMFC and reduce the cost of the catalyst, two approaches are mainly used: one is from the intrinsic activity of the catalyst, the use amount of the noble metal Pt is reduced by changing a carrier, preparing an alloy catalyst and the like, so that the activity and the stability of the catalyst are improved; and the other is to improve the performance of the PEMFC by exploring a new membrane electrode preparation method and preparation process from the viewpoint of membrane electrode and catalyst layer structures. The nano porous carbon material has the advantages of high specific surface area, large pore volume, high chemical and thermal stability, good conductivity and the like. They have received a wide range of attention in a variety of applications (adsorption, catalysis, energy conversion and storage). Zeolitic Imidazolate Frameworks (ZIFs), such as ZIF-67 and ZIF-8, have become effective templates for the production of functional materials with porous structures. This is mainly due to the fact that the carbon skeleton obtained by thermal annealing can confine the in-situ formed metal species to a well-defined morphology, thus synthesizing multifunctional nanomaterials with porous structure, heteroatom dopants and homogeneously distributed metal compounds.

Wherein the ZIF-8 derived amorphous carbon skeleton exhibits high surface area, high porosity and less electron conductivity. ZIF-67 can be converted to a highly graphitic carbon skeleton. Therefore, the bimetallic complex of ZIF-8 and ZIF-67 produced a synergistic effect, synthesizing Co nanoparticles with graphitic carbon coating characterized by high graphitic carbon content and high specific surface area. On the basis, a new ZIF-8@ TA/ZIF-67@ TA is constructed as a precursor, and a material with catalytic performance is calcined. According to the invention, a series of different Co contents are designed and synthesized by regulating and controlling the calcination temperature and the ratio of ZIF-67 to ZIF-8, and the Co and N Co-doped carbon catalyst is prepared by pyrolysis. Electrochemical test studies show that the current density of the catalyst is 0.78 times that of commercial Pt/C in 0.1M KOH and the potential is equal to 0.1V, meanwhile, the reaction process of ORR is 4 electrons in an alkaline medium, and in addition, the electrochemical stability of the catalyst is more excellent than that of the commercial Pt/C catalyst.

Disclosure of Invention

The invention aims to solve the problems of the existing fuel cell catalyst, overcome the defects of the prior art, solve the problems of single precursor obstacle and synthesis cost of the existing fuel cell catalyst, and overcome the defects of high cost, toxicity and the like of a Pt-based catalytic material; based on the unique structure of ZIF-8@ TA/ZIF-67@ TA, a metal organic framework nano composite material for a proton membrane fuel cell is developed, and the nano composite material has the advantages of high initial potential, half-slope potential, excellent limiting current, excellent stability, good methanol tolerance, strong methanol poisoning resistance and the like.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a preparation method of a double MOF connection structure nano composite electrocatalyst for a proton membrane fuel cell comprises the following steps:

(1) dissolving 5.5 g of 2-methylimidazole in 20 mL of deionized water;

(2) 0.45 g of Co (NO) is weighed out₃)₂6H2O dispersed in 5 mL of deionized water;

(3) pouring the 2-methylimidazole solution rapidly into Co²⁺The solution was stirred at room temperature for 6 hours. Washing the obtained product with ethanol and water for several times, and drying to obtain a ZIF-67 nanocrystal;

(4) 3.3 g of 2-methylimidazole are weighed and dissolved in 70 mL of methanol solution;

(5) 1.5 g Zn (NO) are weighed out₃)₂·6H₂O dispersing the mixture in 70 mL of methanol solution;

(6) 2-methylimidazole solution is poured rapidly into Zn²⁺The solution was stirred at room temperature for 24 hours;

(7) washing and centrifuging the obtained product by using a methanol solution, and finally drying to obtain a ZIF-8 crystal;

(8) dispersing 300 mg of ZIF-8 nanocrystals in 10 mL of deionized water, and carrying out ultrasonic treatment for 5 min;

(9) the pH of the TA solution (12 mM, 6 mL) was adjusted to 7.5 with a prepared KOH (6M) solution;

(10) pouring the adjusted TA solution into the ZIF-8 solution, and carrying out ultrasonic treatment for 30 min to obtain a ZIF-8@ TA solution;

(11) the pH of the TA solution (12 mM, 6 mL) was adjusted to 7.5 with a prepared KOH (6M) solution;

(12) pouring the adjusted TA solution into the ZIF-67 solution, and carrying out ultrasonic treatment for 30 min to obtain ZIF-67@ TA;

(13) carrying out ultrasonic treatment on the ZIF-67@ TA solution in the ZIF-8@ TA solution for 30 min, washing the obtained mixed solution with deionized water and methanol for several times, and drying to obtain a precursor;

(14) and carrying out heat treatment on the precursor in an Ar atmosphere, and carrying out thermal annealing to obtain the double MOF connection structure nano composite electrocatalyst (ZIF-8 @ TA/ZIF-67@ TA) for the proton membrane fuel cell.

In the technical scheme, the drying temperature in the step (3) is below 60 ℃, and the drying time is 12 hours;

in the technical scheme, the drying temperature in the step (7) is 80 ℃, the drying time is 12h, and the deformation of the precursor structure is avoided;

in the above technical scheme, the drying temperature in the step (13) is 60 ℃, the drying time is 12 hours, and the deformation of the precursor structure is avoided;

in the technical scheme, the heat treatment temperature in the step (14) is 800 ℃, the reaction time is 3 hours, and the heating rate is controlled to be 1-5 ℃/min, because the heating rate is too high, the structure collapse is easily caused during calcination.

Compared with a commercial Pt/C catalyst, the double-MOF connection structure nano composite electrocatalyst has the following advantages:

(1) the preparation process of the catalyst adopts a thermal decomposition method with simple equipment, simple operation steps, environmental protection and easily controlled reaction conditions, and not only shows high initial potential, half-slope potential, excellent limiting current, excellent stability and good methanol tolerance, but also has the advantages of strong methanol poisoning resistance and the like.

(2) The prepared double MOF nano-material catalyst of the proton membrane fuel cell is compared with a commercial Pt/C catalyst, the two catalysts have similar initial potentials (0.95V vs 0.94V), and the half-slope potential and the limiting current density are both superior to the commercial Pt/C (2.8 mA cm/cm)^-2 vs 2.7 mA cm^-2，5.17 mA cm^-2 vs 6.6 mA cm^-2) The catalyst is superior to commercial Pt/C catalysts as a whole.

(3) The tannic acid molecule of the present invention can bind to the surface of MOFs because it has the ability to coordinate with metal ions and change the surface of MOFs from hydrophobic to hydrophilic (abundant hydroxyl groups can exhibit excellent hydrophilicity and coating ability); the existence of tannic acid on the surface can effectively inhibit the aggregation tendency of the original MOFs material, so that the structure is uniform, and a foundation is provided for good electrocatalysis performance; as a weak organic acid, tannic acid can release free H, and then can permeate into MOFs and destroy the internal skeleton; at the same time, the attached tannic acid macromolecules can clog the exposed surfaces of the MOFs material, thereby protecting the exterior of the MOFs from further etching and shell collapse.

Drawings

FIG. 1 is a ZIF-8@ TA/ZIF-67@ TA appearance chart prepared in accordance with the present invention;

FIG. 2 is an XRD pattern of a ZIF-8@ TA/ZIF-67@ TA sample (scan interval: 5 ° -80 °, step size: 0.02 °, scan rate: 1.5 °/min). (a) XRD patterns of ZIF-8, ZIF-8@ TA, ZIF-67@ TA and ZIF-8@ TA/ZIF-67@ TA calcined at different calcination temperatures (b) at 800 ℃;

FIG. 3 is a scanning electron micrograph of ZIF-8@ TA/ZIF-67@ TA;

FIG. 4 is a transmission electron micrograph and a selected area electron diffractogram of ZIF-8@ TA/ZIF-67@ TA;

FIG. 5 is a ZIF-8@ TA/ZIF-67@ TA initial XPS spectrum full spectrum (a), N (b), C (C), Co (d), Zn (e);

FIG. 6 shows a ZIF-8@ TA/ZIF-67@ TA nanomaterial in N₂And O₂CV plot in saturated 0.1M KOH (sweep range of-0.9-0.1V, scan rate 50 mv/s);

FIG. 7 is a ZIF-8@ TA/ZIF-67@ TA nanomaterial prepared at different temperatures under O₂LSV profile in saturated 0.1M KOH (scan range-0.9-0.1V, scan rate 10 mv/s);

FIG. 8 is a graph of ZIF-8@ TA/ZIF-67@ TA and Pt/C at O for different ZIF-67 loadings₂LSV profile in saturated 0.1M KOH (scan range-0.9-0.1V, scan rate 10 mv/s);

FIG. 9 is an LSV plot of ZIF-8@ TA/ZIF-67@ TA at different speeds (625 rmp, 900 rmp, 1225 rmp, 1600 rmp, 2025 rmp, scan rate 10 mv/s);

FIG. 10 is a K-L equation plot for ZIF-8@ TA/ZIF-67@ TA;

FIG. 11 is a ZIF-8@ TA/ZIF-67@ TA and Pt/C at O₂I-t curves run in saturated 0.1M KOH for long periods of time;

FIG. 12 is an i-t plot of ZIF-8@ TA/ZIF-67@ TA and Pt/C run with methanol addition.

Detailed Description

The invention provides a method for synthesizing a ZIF-8@ TA/ZIF-67@ TA catalyst by a simple thermal decomposition preparation process, which comprises the following steps:

(1) dissolving 5.5 g of 2-methylimidazole in 20 mL of deionized water;

(2) 0.45 g of Co (NO) is weighed out₃)₂·6H₂O dispersing the mixture in 5 mL of deionized water;

(6) quickly pouring the 2-methylimidazole solution into the Zn2+ solution and stirring at room temperature for 24 hours;

(14) and heating the precursor to 800 ℃ at the heating rate of 5 ℃/min in the Ar atmosphere for heat treatment for 3h, and carrying out thermal annealing to obtain the ZIF-8@ TA/ZIF-67@ TA catalyst.

The ZIF-8@ TA/ZIF-67@ TA catalyst is prepared by thermal decomposition.

The invention uses a platinum electrode as a counter electrode, a saturated silver chloride electrode (Ag/AgCl) as a reference electrode and a Pt/C electrode as a working electrode.

The concentration of Nafion added in the preparation process of the catalyst is 5 percent, and the dosage is 15 ul.

The catalyst of the invention is prepared by dispersing 4 mg of the catalyst ink (ink) in 1 mL of mixed solution (250 uL of deionized water, 735 uL of isopropanol and 15uL of 5 wt% Nafion solution) by using a balance. Then gradually dropping 28 uL ink on the surface of the glassy carbon electrode (catalyst loading amount is 0.25 mg cm)^-2) And carrying out an electrocatalysis performance test after naturally drying.

All electrocatalytic performance tests described in the present invention were performed in 0.1M KOH (pH = 13.62) electrolyte, and the experimentally measured potential was converted to a potential relative to a Reversible Hydrogen Electrode (RHE) by the following formula:

the potential values referred to in the present invention are all potentials relative to the reversible hydrogen electrode.

The catalyst of the present invention requires CV activation for 3 cycles before electrochemical testing.

The catalyst is tested at normal temperature, and the influence of large temperature change difference on the performance of the catalyst is prevented.

The invention will be further illustrated with reference to the following specific examples. In order to further clarify the present invention, preferred embodiments of the present invention are described in connection with the examples which are intended to illustrate various features and advantages of the present invention, but not to limit the scope of the invention which is not defined by the claims. In addition, it should be understood that various changes or modifications can be made by those skilled in the art after reading the disclosure of the present invention, and such equivalents also fall within the scope of the invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.

Example 1:

this example shows the synthesis of a ZIF-8@ TA/ZIF-67@ TA catalyst.

(1) Dissolving 5.5 g of 2-methylimidazole in 20 mL of deionized water;

(5) 1.5 g Zn (NO) are weighed out₃)₂·6H₂ O dispersing itIn 70 mL of methanol solution;

(14) and heating the precursor to 800 ℃ at the heating rate of 5 ℃/min in the Ar atmosphere for heat treatment for 3h, and carrying out thermal annealing to obtain a ZIF-8@ TA/ZIF-67@ TA sample.

FIG. 1 is a chart showing the appearance of ZIF-8@ TA/ZIF-67@ TA prepared.

Phase identification and microstructure and structure characterization are carried out on the ZIF-8@ TA/ZIF-67@ TA material obtained in the embodiment: and phase identification is carried out on the prepared material by using a powder X-ray diffractometer and an X-ray photoelectron spectrometer, and the microscopic morphology and the structural characterization are carried out on the obtained material by using a scanning electron microscope and a transmission electron microscope.

FIG. 2 is an XRD pattern (a) of ZIF-8@ TA/ZIF-67@ TA samples at different calcination temperatures (700 ℃, 800 ℃, 900 ℃), and XRD patterns of ZIF-8, ZIF-8@ TA, ZIF-67@ TA and ZIF-8@ TA/ZIF-67@ TA calcined at 800 ℃. (b) (the scanning interval is 5-80 degrees, and the scanning speed is 8 degrees/min). The graph shows that the sample has high purity, no obvious impurity is generated, the crystallization of the synthesized material is good when the diffraction peak is relatively sharp, the catalyst has a peak around 2 theta =26 degrees, and the peak is a characteristic peak of graphitized carbon, which indicates that the catalyst is a carbon material with a certain graphitization degree. Three obvious characteristic diffraction peaks of the Co simple substance corresponding to (111), (200) and (220) surfaces appear at 2 theta =44 °, 51 ° and 76 °, are highly matched with a Co (PDF # 15-0806) card, and the crystallinity of the Co simple substance is gradually enhanced along with the rise of the calcination temperature, so that the Co simple substance conforms to the thermodynamic law of metals. And (b) a phase change process in the synthesis process of the ZIF-8@ TA/ZIF-67@ TA is proved, when TA is added into the ZIF-8 and the ZIF-67, the crystal structure of the MOF is not influenced, the crystallinity of graphite carbon is gradually enhanced, the graphitization degree is improved, the addition of the ZIF-67@ TA into the ZIF-8@ TA is further verified, the respective structures of the ZIF-8@ TA and the ZIF-67@ TA are not damaged, and a ZIF-8@ TA/ZIF-67@ TA sample is synthesized.

FIG. 3 and FIG. 4 are respectively a scanning electron micrograph, a transmission electron micrograph and a selected area electron diffraction pattern of ZIF-8@ TA/ZIF-67@ TA. As can be seen from the figure, the ZIF-8@ TA/ZIF-67@ TA sample powder is composed of spherical particles with a few voids in the middle. The particle size distribution is about 100nm, and the lattice spacing is 0.204 nm, which is beneficial to enhancing the catalytic action of the catalyst.

FIG. 5 is an XPS spectrum survey (a), N (b), C (C), Co (d), Zn (e) spectra of ZIF-8@ TA/ZIF-67@ TA; the graphitic nitrogen atoms are located between the graphitized carbon layers, which can improve the conductivity of the carbon material, and pyrrole nitrogen and pyridine nitrogen can promote the electrochemical reaction. The Co spectrograms are respectively assigned to Co 2p3/2 and Co 2p 1/2. The sample also has peaks at 780.4 eV and 796 eV, and the peak interval is 15.6 eV, which shows that Co in the material is mainly Co₃O₄The form exists. The spectrogram of Zn has two peaks at 1044.7 eV and 1021.6 eV, and the existence of Zn simple substance in ZIF-8@ TA/ZIF-67@ TA is proved.

Example 2:

the embodiment shows the electrochemical performance research of a catalyst which is a nano material ZIF-8@ TA/ZIF-67@ TA.

The catalyst of the inventionThe preparation is that 4 mg of the catalyst ink (ink) is dispersed in 1 mL of mixed solution (250 uL of deionized water, 735 uL of isopropanol and 15uL of 5 wt% Nafion solution) by using a scale. Then gradually dropping 28 uL ink on the surface of the glassy carbon electrode (catalyst loading amount is 0.25 mg cm)^-2) And carrying out an electrocatalysis performance test after naturally drying.

Nafion added in the preparation process of the catalyst is produced by Aldrich sigma company, and the concentration is 5%.

The catalyst is absorbed by a pipette gun to be 7 ul and dropped on a working electrode, the step is repeated for 3 times after the catalyst is naturally aired, then the working electrode slowly enters 0.1M KOH electrolyte saturated by oxygen, bubbles are prevented from being generated on the working electrode in the step, and the electrolyte is continuously introduced into oxygen in the whole testing process to ensure oxygen saturation.

Cyclic voltammetry and linear cyclic voltammetry tests were performed on the catalyst obtained in this example: the cyclic voltammetry test was carried out using an electrochemical workstation manufactured by Pine of the United states, the test voltage sweep range was-0.9-0.1V, the sweep rate was 50 mV/s, and during the test, the cyclic voltammetry test was carried out after 3 cycles of activation with a current density of 50 mV/s. Linear cyclic voltammetry tests were also performed using the Pine electrochemical workstation, with a test voltage sweep range of-0.9-0.1V and a sweep rate of 50 mV/s. The current density of the catalyst material under different rotating speeds can be obtained through rotating speed test, the number of transferred electrons can be obtained by utilizing a K-L equation, the test current density is 10mV/s, and the rotating speeds are 625 rmp, 900 rmp, 1225 rmp, 1600 rmp and 2025 rmp. The stability and the methanol tolerance are also important indexes of the catalyst performance, the test is also completed on an electrochemical workstation, the stability test voltage is-0.189V, and the test time length is 20000 s; the methanol tolerance test voltage was-0.189V, the test duration was 1000 s, and a 2M methanol solution was dropped at 250 s.

FIG. 6 is a ZIF-8@ TA/ZIF-67@ TA catalyst cyclic voltammogram (test voltage sweep range: -0.9-0.1V, sweep rate: 50 mV/s), and we did not detect any significant oxidation or reduction peaks in the nitrogen-saturated electrolyte solution, but only obtained a quasi-rectangular voltammogram typical of a carbon material having a high specific surface area. When in an oxygen saturated electrolyte, a significant cathodic oxygen reduction peak was present at 0.78V, indicating that the ZIF-8@ TA/ZIF-67@ TA catalyst has significant catalytic activity for oxygen reduction reactions.

FIG. 7 is a linear cyclic voltammogram of the ZIF-8@ TA/ZIF-67@ TA catalyst at different temperatures (test voltage range: -0.9-0.1V, scan rate: 50 mV/s), respectively, with the ZIF-8@ TA/ZIF-67@ TA catalyst performing best when the calcination temperature is 800 ℃.

FIG. 8 is a graph of ZIF-8@ TA/ZIF-67@ TA and Pt/C at O for different ZIF-67 loadings₂An LSV diagram (scanning range is-0.9-0.1V and scanning speed is 10 mv/s) in saturated 0.1M KOH, under the calcination temperature of 800 ℃, ZIF-8@ TA/ZIF-67@ TA has different mixture ratios and an LSV diagram of a Pt/C catalyst, and it can be seen that four materials of ZIF-8@ TA/ZIF-67@ TA have the same initial potential, the catalytic performance of the catalyst tends to increase and decrease along with the increase of the content of ZIF-67, and the ultimate current density of the catalyst is the largest when the loading of the ZIF-67 is 500mg, which is probably because the catalytic performance of the materials is different due to different contents of ZIF-67 and oxygen.

FIG. 9 is a plot of LSV (sweep rate: 10 mV/s) for the catalyst CoNi @ TA/B at various rpm conditions (400 rpm, 625 rpm, 900 rpm, 1225 rpm, 1600 rpm, 2500 rpm), and it can be seen that the current density also shows a tendency to increase gradually as the rpm increases, primarily due to the fact that the increasing rpm effectively shortens the diffusion layer of the oxygen reduction reaction. A series of oxygen reduction curves of the catalyst show a better diffusion-limiting current platform, which means that the catalytic active sites of the catalyst are distributed more uniformly, and the speed of the oxygen reduction process is improved.

FIG. 10 is a K-L plot of ZIF-8@ TA/ZIF-67@ TA with the slope of the plot remaining substantially constant over the entire sweep potential range, meaning that oxygen reduction under the influence of the catalyst has the same number of transferred electrons at different potentials. According to the RRDE test result, the ORR electron transfer number (n) of the catalyst ZIF-8@ TA/ZIF-67@ TA in the potential range of 0.2V to 0.4V is calculated to be 3.69 to 3.56, which shows that the catalyst prepared by the catalyst is catalyzed by the transfer path of 4 electrons in an alkaline electrolyte.

FIG. 11 is a graph of ZIF-8@ TA/ZIF-67@ TA and Pt/C tested by chronoamperometry after 20000 s of testing for the catalyst ZIF-8@ TA/ZIF-67@ TA, the initial current density for the Pt/C catalyst is significantly lost 23% while the ZIF-8@ TA/ZIF-67@ TA catalyst is only reduced by 13%. Although not much apart, it can still be shown that the catalysts we have produced are still superior to commercial Pt/C.

FIG. 12 is a graph of methanol resistance of the ZIF-8@ TA/ZIF-67@ TA and commercial 20% Pt/C catalyst, which was found to exhibit a very significant instantaneous jump in current after 250 s addition of 2M methanol, with a significant drop in ORR current to 0.3 mA cm-2 after recovery, whereas the ZIF-8300@ TA/ZIF-67500@ TA catalyst showed little reaction and little current effect, indicating some resistance to methanol.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims

1. A preparation method of a double MOF connection structure nano composite electrocatalyst for a proton membrane fuel cell is characterized by comprising the following steps: the preparation method comprises the following steps:

(1) dissolving 2-methylimidazole in deionized water;

(2) then adding Co (NO)₃)₂·6H₂O is dispersed in deionized water;

(3) quickly pouring the 2-methylimidazole solution obtained in the step (1) into the Co obtained in the step (2)²⁺Stirring the solution for 6 hours at room temperature, washing the obtained product with ethanol and water for several times, and drying to obtain ZIF-67 nano crystals for later use;

(4) dissolving 2-methylimidazole in a methanol solution;

(5) adding Zn (NO)₃)₂·6H₂O is dispersed in the methanol solution;

(6) quickly pouring the 2-methylimidazole solution in the step (4) into the Zn in the step (5)²⁺The solution was stirred at room temperature for 24 hours;

(7) washing and centrifuging the product obtained in the step (6) by using a methanol solution, and finally drying to obtain a ZIF-8 crystal for later use;

(8) dispersing the ZIF-8 nanocrystals obtained in the step (7) in deionized water, and performing ultrasonic treatment for 5 min;

(9) adjusting the pH value of the TA solution to 7.5 by using 6M KOH solution;

(10) pouring the TA solution adjusted in the step (9) into the ZIF-8 solution, and carrying out ultrasonic treatment for 30 min to obtain the ZIF-8@ TA solution;

(11) adjusting the pH value of the TA solution to 7.5 by using 6M KOH solution;

(12) pouring the TA solution adjusted in the step (11) into a ZIF-67 solution, and carrying out ultrasonic treatment for 30 min to obtain ZIF-67@ TA;

(13) rapidly mixing the ZIF-67@ TA solution in the step (12) with the ZIF-8@ TA solution in the step (10), performing ultrasonic treatment for 30 min, washing the obtained product with deionized water and methanol respectively, and drying to obtain a precursor;

(14) and (4) carrying out heat treatment on the precursor in the step (13) in an Ar atmosphere and annealing to obtain the double MOF connection structure nano composite electrocatalyst for the proton membrane fuel cell.

2. The method of claim 1, wherein: and (4) drying at the temperature of 60 ℃ for 12h in the step (3).

3. The method of claim 1, wherein: and (4) drying at the temperature of 80 ℃ for 12h in the step (7).

4. The method of claim 1, wherein: and (4) drying at the temperature of 60 ℃ for 12h in the step (13).

5. The method of claim 1, wherein: the heat treatment and annealing in the step (14) are specifically as follows: heating to 800 deg.C at a rate of 5 deg.C/min, maintaining for 3 hr, and naturally cooling to room temperature.

6. A double MOF-linked structure nanocomposite electrocatalyst for proton membrane fuel cell prepared by the preparation method according to any one of claims 1 to 5, wherein: the catalyst is a ZIF-8@ TA/ZIF-67@ TA nano material.