CN113451592A - Carbon-based catalyst with hierarchical pore structure and preparation method and application thereof - Google Patents

Abstract

The invention discloses a carbon material with a hierarchical pore structure and a preparation method and application thereof.A P123 soft template micelle bead and 2-methylimidazole hydrogen bond self-assembly is adopted, a cobalt nitrate or zinc nitrate solution with a certain proportion is added, then hydrothermal reaction is carried out at 40 ℃, carbonization treatment is carried out after centrifugal drying, and P123 is decomposed and volatilized in the carbonization process, so that the carbon-based catalyst with the micropore-mesopore composite hierarchical pore structure is finally formed. The prepared catalyst has excellent catalytic performance, and a zinc air battery and a proton exchange membrane fuel cell assembled by using the catalyst have good performance, and are suitable for popularization and application.

Description

Carbon-based catalyst with hierarchical pore structure and preparation method and application thereof

Technical Field

The invention relates to the technical field of fuel cells, in particular to a carbon-based catalyst with a hierarchical pore structure, and a preparation method and application thereof.

Background

In recent years, environmental problems are gradually focused by overuse of fossil fuels, and researchers are also more and more dedicated to research and develop environment-friendly and energy-saving clean energy. Proton exchange membrane fuel cells and zinc-air cells have the characteristics of high specific energy, high efficiency and low pollution, are considered as two very promising new energy sources and are gradually valued by scientific research units. Both cells use noble metal catalysts to accelerate their electrochemical reactions and are therefore relatively expensive. As such, both batteries require an efficient and inexpensive catalyst to accelerate their commercialization.

The MOF material (metal-organic framework material) is an organic matter formed by coordination and self-assembly of a metal active center and an organic ligand, and has wide application in the fields of catalysis, gas storage and separation, sensing, carrier application and the like. The MOF material precursor contains a nitrogen source and a metal source, so that the MOF material precursor can be used as a transition metal-nitrogen-carbon catalyst after carbonization treatment. By controlling the composition and preparation process, we can obtain a wide variety of MOF-derived catalyst materials. Although MOF materials have many advantages themselves, the catalytic performance of porous carbon-based catalysts prepared by direct carbonization of MOF materials is less than ideal and still far from commercial Pt/C.

A Chinese patent application with publication number CN 109950555A discloses a cobalt @ cobaltosic oxide nanoparticle embedded nitrogen-doped carbon nanotube material and a preparation method and application thereof, wherein the preparation method comprises the following steps: 1) mixing a cobalt source, P123, a nitrogen source and a solvent to prepare a precursor solution, and then removing the solvent in the precursor solution to obtain a mixture; wherein the cobalt source is selected from at least one of cobalt nitrate hexahydrate, cobalt oxalate and cobalt chloride, the solvent is selected from at least one of deionized water, ethanol and methanol, and the nitrogen source is selected from at least one of melamine, urea and 2-methylimidazole. 2) The mixture was milled to give a powder, which was then calcined in the presence of a shielding gas to produce Co @ Co3O4 nanoparticles embedded in nitrogen doped carbon nanotube material. The preparation method is low in cost and simple in process, and breaks through the conventional loading form to prepare the Co @ Co3O4 nano particles which are uniform and controllable in appearance and higher in particle dispersion degree and are embedded into the nitrogen-doped carbon nano tube material, so that the Co @ Co3O4 nano particles embedded into the nitrogen-doped carbon nano tube material can be used as a fuel cell cathode catalyst.

However, the existing MOF-derived catalysts have not been studied in depth on the pore structure, especially the structure of the microporous composite mesopores.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a hierarchical pore structure carbon-based catalyst with excellent catalytic activity and a microporous composite mesoporous structure, and a preparation method and application thereof.

In order to achieve the purpose, the invention adopts the following technical scheme.

A preparation method of a carbon-based catalyst with a hierarchical pore structure is characterized by comprising the following steps: 1) dissolving P123 in deionized water to form a clear solution, then dissolving 2-methylimidazole in deionized water, pouring into the clear solution, and stirring for reaction to obtain a mixed solution A; 2) dissolving transition metal nitrate in deionized water, adding the solution into the mixed solution A, stirring and reacting for a period of time to obtain a mixed solution B, then pouring the mixed solution B into a polytetrafluoroethylene reaction kettle, and carrying out heat preservation reaction at 40 +/-5 ℃ for 24 +/-4 hours; 3) centrifuging and cleaning the reaction product in the step 2), and then putting the reaction product into a vacuum drying oven to dry at the temperature of 60 +/-5 ℃; 4) under the protection of inert gas, carrying out high-temperature carbonization treatment on the dried product obtained in the step 3) to obtain the carbon-based catalyst with the hierarchical pore structure.

More preferably, in step 1), the mass ratio of P123 to 2-methylimidazole is 1: 5-10.

More preferably, in step 1), the P123 is dissolved in deionized water and then forms a clear solution by heating in a water bath, wherein the temperature of the water bath is 40 ± 5 ℃.

More preferably, in step 1), the stirring reaction time of the 2-methylimidazole and the P123 is 6 to 12 hours.

More preferably, in the step 2), the transition metal nitrate is cobalt nitrate hexahydrate and zinc nitrate hexahydrate which are mixed according to a proportion, and the molar ratio of the cobalt nitrate hexahydrate to the zinc nitrate hexahydrate is 0: 1-1: 1.

it is more preferable that the stirring reaction time of the transition metal nitrate with the mixed solution A in the step 2) is 8 to 12 min.

More preferably, in step 3), the centrifugation and washing method is: centrifuging by a centrifuge and washing by deionized water and ethanol for more than 3 times respectively.

More preferably, in step 4), the carbonization process is: before the temperature rise, protective gas is introduced to exhaust the air in the tube furnace, then the temperature in the tube furnace is raised to 400 ℃ from the room temperature at the temperature rise rate of 1-3 ℃ per minute and is kept for 90 +/-5 min, then the temperature in the tube furnace is continuously raised to 600 ℃ at the temperature rise rate of 1-3 ℃ per minute, and then the temperature in the tube furnace is raised to 900 ℃ at the temperature rise rate of 3-5 ℃ per minute and is kept for a period of time.

The invention also provides the carbon-based catalyst with the hierarchical pore structure prepared by the preparation method. The carbon-based catalyst with the hierarchical pore structure prepared according to the scheme has good catalytic performance.

The invention also provides the use of a carbon-based catalyst having a hierarchical pore structure as described above in a fuel cell.

Compared with the prior art, the invention has the following advantages and beneficial effects.

The method comprises the steps of self-assembling micelle globules of a P123 soft template and 2-methylimidazole hydrogen bonds, adding cobalt nitrate or zinc nitrate solution in a corresponding proportion, carrying out hydrothermal reaction, carrying out carbonization treatment after centrifugal drying, and decomposing and volatilizing P123 in the carbonization process to finally form the microporous-mesoporous composite carbon-based catalyst with the hierarchical pore structure. The hierarchical pore structure can effectively improve the specific surface area of the catalyst, is beneficial to exposing the active sites of the catalyst to the maximum extent, and can provide channels for the rapid transfer of reaction substances and reduce the diffusion resistance of oxygen.

And secondly, the addition of a nitrogen source and a cobalt source enables the MOF precursor to have the advantages of a ZIF-8 structure and a ZIF-67 structure, and meanwhile, the performance of the ORR catalyst is effectively improved by combining a hierarchical pore structure formed by P123, and the ORR catalyst has excellent stability, methanol resistance and OER performance besides the ORR performance, is a bifunctional non-noble metal catalyst with a very promising performance, and has the performance equivalent to or even more excellent than that of commercial Pt/C.

The preparation process and reaction conditions related by the invention are simple, high-temperature and high-pressure conditions are not needed, the production cost is low, and the preparation method is suitable for popularization and application.

Drawings

FIG. 1 shows LSV spectra for carbon-based catalysts having hierarchical pore structures made in examples 1-4 of the present invention.

Fig. 2 a-2 d are TEM, HRTEM, and elemental distribution plots for carbon-based catalysts with hierarchical pore structures prepared in example 3 of the present invention.

Detailed Description

The following describes the embodiments of the present invention with reference to the drawings of the specification, so that the technical solutions and the advantages thereof are more clear and clear. The embodiments described below are exemplary and are intended to be illustrative of the invention, but are not to be construed as limiting the invention.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

A carbon-based catalyst with a hierarchical pore structure is prepared according to the following principle: the preparation method comprises the steps of self-assembling the P123 soft template micelle globules and 2-methylimidazole hydrogen bonds, adding a certain proportion of cobalt nitrate or zinc nitrate solution, carrying out hydrothermal reaction at 40 +/-5 ℃, carrying out carbonization treatment after centrifugal drying, and decomposing and volatilizing the P123 in the carbonization process to finally form the microporous-mesoporous composite carbon-based catalyst with the hierarchical pore structure.

Wherein, P123 is a triblock copolymer, which is fully called as follows: a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer having the molecular formula: PEO-PPO-PEO. The specific shape of the micelle globule is a spherical structure formed by outward divergence of a plurality of bundles, and is a common product structure in the field of templates.

According to the invention, P123 is used as a soft template and an additive for promoting 2-methylimidazole, cobalt nitrate and zinc nitrate to form MOF, and the proportion of nitrate in a precursor is changed, so that the obtained MOF material is carbonized at high temperature to form the microporous-mesoporous composite hierarchical pore structure catalyst. The prepared MOF derivative catalyst has excellent ORR and OER catalytic performances under an alkaline condition, the assembled zinc-air battery also has excellent electrochemical performance, and compared with the performance of the zinc-air battery assembled by taking Pt/C as a catalyst, the catalyst has the advantages of better catalytic performance, higher stability, simple manufacturing method, low cost and excellent structure, and is suitable for popularization and application.

In the following examples, various reagents used were commercially available chemical reagents or industrial products unless otherwise specified.

Example 1.

A carbon-based catalyst having a hierarchical pore structure is prepared by a method comprising the following steps.

1) 0.200g P123 was dissolved in 48ml of deionized water and placed in a 40 + -5 deg.C water bath with stirring to form a clear solution, and then 1.5000g of 2-methylimidazole was dissolved in 10ml of deionized water and poured into the clear solution and stirred for another 12 hours to obtain a mixed solution A.

2) Dissolving 2 mmol of zinc nitrate hexahydrate in 5ml of deionized water, adding the solution into the mixed solution A prepared in the step 1), and stirring for 10 +/-2 min to obtain a mixed solution B; the mixed solution B was then poured into a 100 ml Teflon reaction kettle and incubated at 40 + -5 deg.C for 24 + -4 h.

3) Centrifuging the reaction product in the step 2) by using a centrifugal machine, washing the reaction product by using deionized water and ethanol for 3 times respectively, then putting the reaction product into a vacuum drying oven, drying the reaction product at the temperature of 60 +/-5 ℃, and drying the reaction product to obtain a synthetic product, wherein the synthetic product is represented by HZIF-100 Zn.

4) And putting the synthesized product HZIF-100Zn into a high-temperature tube furnace for carbonization, and introducing high-purity nitrogen all the time in the carbonization process to avoid the carbon material from being oxidized. The specific carbonization process is as follows: introducing high-purity nitrogen for 1h to exhaust air in the tubular furnace before carbonization heating, then heating the tubular furnace from room temperature to 400 ℃ at the heating rate of 1 ℃ per minute and preserving heat for 90 min, then continuously heating to 600 ℃ at the heating rate of 2 ℃ per minute, then heating to 900 ℃ at the heating rate of 5 ℃ per minute and preserving heat for 3 h. The carbonized carbon-based catalyst product is represented by HC-100 Zn.

The graded pore structure carbon-based catalyst prepared in this example was subjected to electrochemical testing and had an oxygen reduction half-slope potential of around 0.81V (vs.

Example 2.

A carbon-based catalyst having a hierarchical pore structure is prepared by a method comprising the following steps.

1) 0.232g P123 was dissolved in 48ml of deionized water and placed in a 40 + -5 deg.C water bath with stirring to form a clear solution, and then 1.6422g of 2-methylimidazole was dissolved in 10ml of deionized water and poured into the above clear solution with stirring for 8 hours to obtain a mixed solution A.

2) Dissolving 0.1 mmol of zinc nitrate hexahydrate and 1.9mmol of cobalt nitrate hexahydrate in 5ml of deionized water, adding the mixed solution A, continuously stirring for 10 +/-2 min to obtain a mixed solution B, and then pouring the mixed solution B into a 100 ml of polytetrafluoroethylene reaction kettle, and keeping the temperature at 40 +/-5 ℃ for 24 +/-4 h.

3) Centrifuging the reaction product in the step 2) by using a centrifugal machine, washing the reaction product by using deionized water and ethanol for 3 times respectively, then putting the reaction product into a vacuum drying oven, drying the reaction product at the temperature of 60 +/-5 ℃, and drying the reaction product to obtain a synthetic product, wherein the synthetic product is represented by HZIF-5Co95 Zn.

4) And putting the synthesized product HZIF-5Co95Zn into a high-temperature tube furnace for carbonization, and introducing high-purity nitrogen all the time in the carbonization process to avoid the carbon material from being oxidized. The specific carbonization process is as follows: before the temperature rise, 1h of high-purity nitrogen is introduced to exhaust the air in the tube furnace, then the temperature in the tube furnace is raised to 400 ℃ from the room temperature at the temperature rise rate of 1 ℃ per minute and is kept for 90 +/-5 min, then the temperature in the tube furnace is continuously raised to 600 ℃ at the temperature rise rate of 1 ℃ per minute, and then the temperature in the tube furnace is raised to 900 ℃ at the temperature rise rate of 5 ℃ per minute and is kept for 3 h. The carbonized carbon-based catalyst product is denoted by HC-5 Co95 Zn.

The TEM, HRTEM, and elemental distribution plots for the carbon-based catalyst with hierarchical pore structure prepared in this example are shown in fig. 2 a-2 d. In which, fig. 2a and fig. 2b are TEM images of 200nm and 100nm at two different multiples, respectively, and it can be clearly seen from these two images that the carbon-based catalyst product HC-5 Co95Zn prepared in this example is not a dense structure, but is distributed with a rich mesoporous structure, and the pore diameter of the mesopores is about 20 nm.

Fig. 2C is an HRTEM image. From this figure, the abundant micropores and the Co lattice fringes of about 0.2 nm, corresponding to the Co (111) planes, are clearly visible. The catalyst with the hierarchical pore structure of the microporous composite mesopores has larger specific surface area, is beneficial to exposing the active sites of the catalyst to the maximum extent, and can provide channels for the rapid transfer of reaction substances and reduce the diffusion resistance of oxygen.

FIG. 2d is a Mapping diagram of element distribution. It is evident from this figure that both C, N and Co are uniformly distributed, which facilitates a large number of rapid reactions of active sites compared to atomic agglomeration. The graded pore structure carbon-based catalyst prepared in this example was subjected to electrochemical testing and had an oxygen reduction half-slope potential of around 0.88V (vs.

Example 3.

A carbon-based catalyst having a hierarchical pore structure is prepared by a method comprising the following steps.

1) 0.232g P123 was dissolved in 48ml of deionized water and placed in a 40 + -5 deg.C water bath with stirring to form a clear solution, and then 2.232g of 2-methylimidazole was dissolved in 10ml of deionized water and poured into the above solution with stirring for 6 hours to obtain a mixed solution A.

2) Dissolving 1mmol of zinc nitrate hexahydrate and 1mmol of cobalt nitrate hexahydrate in 5ml of deionized water, adding the mixture into the mixed solution A, continuously stirring for 10 +/-2 min to obtain a mixed solution B, and then pouring the mixed solution B into a 100 ml of polytetrafluoroethylene reaction kettle and preserving the temperature for 24 +/-4 h at 40 +/-5 ℃.

3) And (3) centrifuging the reaction product in the step 2) by using a centrifugal machine, washing the reaction product by using deionized water and ethanol for 3 times respectively, then putting the reaction product into a vacuum drying oven, drying the reaction product at 60 +/-5 ℃, and drying the reaction product to obtain a synthetic product, wherein the synthetic product is represented by HZIF-50Co50 Zn.

4) And putting the synthesized product HZIF-50Co50Zn into a high-temperature tube furnace for carbonization, and introducing high-purity nitrogen all the time in the carbonization process to avoid the carbon material from being oxidized. The specific carbonization process is as follows: before the temperature rise, 1h of high-purity nitrogen is introduced to exhaust the air in the tube furnace, then the temperature in the tube furnace is raised to 400 ℃ from the room temperature at the heating rate of 3 ℃ per minute and is kept for 90 +/-5 min, then the temperature in the tube furnace is continuously raised to 600 ℃ at the heating rate of 2 ℃ per minute, and then the temperature in the tube furnace is raised to 900 ℃ at the heating rate of 5 ℃ per minute and is kept for 3 h. The carbonized product is represented by HC-50 Co50 Zn.

The graded pore structure carbon-based catalyst prepared in this example was subjected to electrochemical testing and had an oxygen reduction half-slope potential of about 0.86V (vs.

Comparative example 1.

A carbon-based catalyst having a hierarchical pore structure is prepared by a method comprising the following steps.

1) 1.6422g of 2-methylimidazole are dissolved in 10ml of methanol and stirred for 8 h.

2) 0.1 mmol of zinc nitrate hexahydrate and 1.9mmol of cobalt nitrate hexahydrate are dissolved in 5ml of methanol and added to the solution obtained in step 1) and stirred for 10. + -. 2min, then poured into a 100 ml of polytetrafluoroethylene reaction vessel and incubated at 40. + -. 5 ℃ for 24. + -. h.

3) Centrifuging the reaction product obtained in the step 2) by using a centrifugal machine, washing the reaction product by using deionized water and ethanol for 3 times respectively, then putting the reaction product into a vacuum drying oven to dry at the temperature of 60 +/-5 ℃, and expressing the dried product by using ZIF-5Co95 Zn.

4) And (3) placing the synthesized ZIF-5Co95Zn in a high-temperature tube furnace, introducing high-purity nitrogen all the time in the carbonization process to avoid the carbon material from being oxidized, and introducing 1h of high-purity nitrogen to exhaust the air in the tube furnace before heating. Raising the temperature from room temperature to 400 ℃ at a heating rate of 1 ℃ per minute and keeping the temperature for 90 min, then continuing to raise the temperature to 600 ℃ at a heating rate of 1 ℃ per minute, raising the temperature to 900 ℃ at a heating rate of 5 ℃ per minute and keeping the temperature for 3 h. The carbonized product is represented by C-5Co95 Zn.

In the preparation process of the catalyst, P123 is not added, the solvent is replaced by absolute methanol from deionized water, the catalyst is named ZIF-5Co95Zn, and the catalyst formed by carbonizing the material is named C-5Co95 Zn. The graded pore structure carbon-based catalyst prepared in this example was subjected to electrochemical testing and had an oxygen reduction half-slope potential of around 0.85V (vs.

The oxygen reduction LSV curves for the carbon-based catalysts with hierarchical pore structures prepared in examples 1-4 are shown in fig. 1, from which it can be seen that: example 3 is an optimal ratio of cobalt nitrate hexahydrate to zinc nitrate hexahydrate. P123 acts as a pore former with the aim of forming a mesoporous structure in a hierarchical pore structure, and at an optimal CoZn ratio, the electrochemical performance deteriorates without the addition of P123.

It will be appreciated by those skilled in the art from the foregoing description of construction and principles that the invention is not limited to the specific embodiments described above, and that modifications and substitutions based on the teachings of the art may be made without departing from the scope of the invention as defined by the appended claims and their equivalents. The details not described in the detailed description are prior art or common general knowledge.

Claims (10)

1. A preparation method of a carbon-based catalyst with a hierarchical pore structure is characterized by comprising the following steps:

1) dissolving P123 in deionized water to form a clear solution, then dissolving 2-methylimidazole in deionized water, pouring into the clear solution, and stirring for reaction to obtain a mixed solution A;

2) dissolving transition metal nitrate in deionized water, adding the solution into the mixed solution A, stirring and reacting for a period of time to obtain a mixed solution B, then pouring the mixed solution B into a polytetrafluoroethylene reaction kettle, and carrying out heat preservation reaction at 40 +/-5 ℃ for 24 +/-4 hours;

3) centrifuging and cleaning the reaction product in the step 2), and then putting the reaction product into a vacuum drying oven to dry at the temperature of 60 +/-5 ℃;

4) under the protection of inert gas, carrying out high-temperature carbonization treatment on the dried product obtained in the step 3) to obtain the carbon-based catalyst with the hierarchical pore structure.

2. The method of claim 1, wherein in step 1), the mass ratio of the P123 to the 2-methylimidazole is 1: 5-10.

3. The method of claim 1, wherein in step 1), the P123 is dissolved in deionized water and then heated in a water bath to form a clear solution, and the temperature of the water bath is 40 ± 5 ℃.

4. The method of claim 1, wherein the stirring reaction time of 2-methylimidazole with P123 in step 1) is 6-12 h.

5. The method of claim 1, wherein in the step 2), the transition metal nitrate is cobalt nitrate hexahydrate and zinc nitrate hexahydrate which are mixed in proportion, and the molar ratio of the cobalt nitrate hexahydrate to the zinc nitrate hexahydrate is 0: 1-1: 1.

6. the method of claim 1, wherein the stirring reaction time of the transition metal nitrate with the mixed solution A in the step 2) is 8-12 min.

7. The method for preparing a carbon-based catalyst with hierarchical pore structure according to claim 1, wherein in the step 3), the manner of centrifugation and washing is as follows: centrifuging by a centrifuge and washing by deionized water and ethanol for more than 3 times respectively.

8. The method of claim 1, wherein in the step 4), the carbonization process is as follows: before the temperature rise, protective gas is introduced to exhaust the air in the tube furnace, then the temperature in the tube furnace is raised to 400 ℃ from the room temperature at the temperature rise rate of 1-3 ℃ per minute and is kept for 90 +/-5 min, then the temperature in the tube furnace is continuously raised to 600 ℃ at the temperature rise rate of 1-3 ℃ per minute, and then the temperature in the tube furnace is raised to 900 ℃ at the temperature rise rate of 3-5 ℃ per minute and is kept for a period of time.

9. A carbon-based catalyst having a hierarchical pore structure prepared by the method of any one of claims 1 to 8.

10. Use of a carbon-based catalyst having a hierarchical pore structure according to claim 9 in a fuel cell.

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