CN112993287A

CN112993287A - Nonmetal catalyst and preparation and application thereof

Info

Publication number: CN112993287A
Application number: CN201911275020.9A
Authority: CN
Inventors: 王素力; 许新龙; 张子楠; 孙公权
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2019-12-12
Filing date: 2019-12-12
Publication date: 2021-06-18
Anticipated expiration: 2039-12-12
Also published as: CN112993287B

Abstract

The invention relates to a preparation method of a non-metal catalyst, wherein the catalyst is obtained by preparing a core-shell structure precursor of zinc oxide nano particles subjected to zeolite imidazole ester framework (ZIF) coating vulcanization or selenization treatment and then performing one-step pyrolysis, and has high electrocatalytic oxygen reduction activity in an alkaline electrolyte. The preparation process is simple, the core can be reduced and volatilized in the heat treatment process, and extra etching treatment is not needed; the pore structure of the catalyst can be changed by adjusting the size of the core and the thickness of the shell in the precursor, so that the catalytic performance can be regulated and controlled; the activity can also be improved by modifying the nucleus to incorporate heteroatoms such as sulfur; as a non-metal catalyst, the catalyst has no problems of metal loss, aggregation, Oswald curing and the like, and has good stability; has high oxygen reduction performance and poisoning resistance performance, and has wide application prospect in alkaline polymer electrolyte membrane fuel cells and metal air cells.

Description

Nonmetal catalyst and preparation and application thereof

Technical Field

The invention belongs to the technical field of catalysts and preparation thereof, and particularly relates to an electrocatalyst for an oxygen reduction reaction of a cathode of an alkaline polymer electrolyte membrane fuel cell or a metal-air fuel cell.

Background

The non-metal catalyst has the advantages of low cost, good stability, good methanol permeation resistance, CO poisoning resistance and the like, and has good application prospect.

In the non-metal catalyst, micropores are required to provide a high specific surface area to improve the active site density of the catalyst, and mesopores are required to be introduced to provide channels for the transmission of reactants and products. The zeolite imidazole ester framework material has a rich microporous structure and is widely applied to the preparation of nonmetal catalysts in recent years. However, the material is lack of mesopores, and mesopores can be introduced into the material by introducing a mesopore template and then performing acid and alkali etching, but the preparation process is complex.

Disclosure of Invention

The invention provides a non-metal catalyst and a preparation method thereof aiming at the defects of the non-metal catalyst and the preparation technology thereof, and the invention is realized by adopting the following specific scheme:

a non-metallic catalyst characterized by: the carbon-doped hollow fiber is hollow particles, mainly comprises carbon, is doped with nitrogen and one or more than two of sulfur and selenium, and the atomic percent of nitrogen is 2-12%, preferably 6-9%; the atomic percentage of sulphur and/or selenium is between 0.5 and 6 percent, preferably between 1 and 3 percent; the mesoporous particle has a micropore and mesoporous hierarchical pore structure, wherein the micropore is positioned on the wall of the particle, the diameter of the micropore is 1-2nm, preferably 1.2-1.4nm, the hollow part of the particle is mesoporous, the diameter of the mesopore is 3-30nm, preferably 4-6nm, and the pore volume of the mesopore accounts for 10-60% of the total pore volume, preferably 25-40%. The zinc oxide nano-particle is obtained by carbonizing a precursor, wherein the precursor is a core-shell structure in which the outer surface of a zinc oxide nano-particle is sequentially coated with a zinc sulfide layer and/or a zinc selenide layer and a zeolite imidazole ester framework (ZIF) layer, and the mass percentage of the zinc sulfide layer and/or the zinc selenide layer is 10-30%, preferably 15-25%. The mass percentage of the ZIF shell in the ZIF shell is 10-90%, preferably 40-50%. The nitrogen exists in the form of one or more of pyridine nitrogen, pyrrole nitrogen, graphitized nitrogen and nitrogen oxide.

The preparation method comprises the following steps of,

(1) preparing a ZnO template: dissolving zinc salt in diethylene glycol, heating and stirring, centrifuging, washing and drying to obtain a ZnO template;

(2) coating zinc sulfide and/or zinc selenide layer: carrying out vulcanization/selenylation treatment on the ZnO template obtained in the step (1) by using a sulfur raw material and selenium principle;

(3) preparing a precursor: dissolving imidazole ligand in a solvent, adding the ZnO template coated with the zinc sulfide and/or zinc selenide layer obtained in the step (2), and heating after ultrasonic dispersion; then obtaining a precursor through centrifugation, washing and vacuum drying;

(4) and (3) heat treatment: and (4) carrying out high-temperature carbonization treatment on the catalyst precursor obtained in the step (3) in an inert atmosphere to obtain the non-metal catalyst.

The zinc salt in the step (1) is one or more than two of zinc nitrate, zinc acetate, zinc sulfate and zinc chloride; the heating temperature is 100-180 ℃, and the time is 0.5-2 h. In the vulcanization method in the step (2), the sulfur raw material is one or more than two of sodium sulfide or thioacetamide, and the method comprises the steps of dissolving the sulfur raw material in water, adding ZnO, and carrying out hydrothermal treatment at the temperature of 60-120 ℃ for 0.5-3 h. In the selenizing method, the selenium raw material is elemental selenium, and the method is to mix and heat the elemental selenium and ZnO at the temperature of 600-900 ℃ for 10-30 min. In the step (3), the solvent is one or more than two of methanol, ethanol, water and N, N-dimethylformamide; the imidazole ligand is one or more than two of imidazole, 2-methylimidazole and benzimidazole; the concentration of imidazole ligand is 0.01-1M, preferably 0.02-0.05M; the heating temperature is 40-80 ℃ and the time is 0.5-10 h. In the step (4), the inert atmosphere is one or a mixture of more than two of nitrogen and argon: the high-temperature carbonization treatment process in the step (4) is to heat the mixture from room temperature or drying humidity to 900-1100 ℃ at the heating rate of 5 ℃/min, keep the mixture for 1-3h, cool the mixture to 300 ℃ at the cooling rate of 1-10 ℃/min, and then naturally cool or naturally cool the mixture.

The catalyst can be used as an electrocatalyst for the oxygen reduction reaction of a cathode of an alkaline polymer electrolyte membrane fuel cell or a metal-air fuel cell.

Drawings

FIG. 1 is a schematic diagram of the preparation process and principle of the sulfur-doped non-metallic catalyst of example 1.

FIG. 2 shows XRD diffraction patterns of ZnO templates and precursors of comparative examples 1 and 2.

Figure 3 XRD diffractogram of example 1.

FIG. 4 shows the nitrogen adsorption/desorption curves of the nitrogen-carbon material of example 1.

FIG. 5 is a graph showing the pore size distribution of the nitrogen-carbon material of example 1.

FIG. 6 oxygen reduction LSV curves for comparative examples 1, 2 and examples 1, 2. The LSV curve was tested in oxygen saturated 0.1M KOH electrolyte using a three electrode system, the catalyst was coated on a rotating disk electrode as the working electrode with a loading of 200mg cm^-2The graphite rod is used as a counter electrode, the saturated calomel electrode is used as a reference electrode, and the potential in the figure is corrected to be the potential relative to the reversible hydrogen electrode. Because the material has high specific surface area and large double-layer capacitance, the background current (double-layer charging current) measured in a saturated nitrogen electrolyte is deducted from a curve in order to avoid the influence of the double-layer capacitance and accurately reflect the magnitude of the oxygen reduction current.

Detailed Description

Comparative example 1

3.26g of zinc nitrate hexahydrate was weighed out and dissolved in 100ml of methanol in a beaker to prepare a solution A, 6.52g of 2-methylimidazole was weighed out and dissolved in 100ml of methanol to prepare a solution B, and the two solutions were placed on a magnetic stirrer at room temperature and stirred uniformly. Slowly adding the solution A into the solution B, stirring for 1h at room temperature, and standing overnight. Then centrifuging, washing and drying at the temperature of 60 ℃ in vacuum to obtain the product ZIF-8.

The prepared ZIF-8 was pyrolyzed in a tubular furnace under nitrogen atmosphere. Keeping the gas flow rate at 300ml/min, increasing the temperature to 900 ℃ at the temperature rise rate of 5 ℃/min, keeping the temperature at the target temperature for 3h, and then reducing the temperature for 60min to 300 ℃. And taking out the catalyst after the catalyst is cooled to room temperature to obtain the product, namely the nitrogen-doped carbon non-metal catalyst NC-900.

The catalyst is characterized by XPS and BET, N elements are doped in the catalyst, the types of the N elements are pyridine type, pyrrole type and graphite type, but the proportion of mesopores is only 3.7%, and the electrocatalysis performance is poor.

Comparative example 2

5.4g of zinc acetate was weighed out and dissolved in 200ml of diethylene glycol, and stirred at 160 ℃ for 1 hour. Cooling to room temperature, centrifuging, washing, and vacuum drying at 60 ℃ for 8h to obtain the product, namely the ZnO nanosphere.

2-methylimidazole (0.04105g) is dissolved in 10ml of methanol, 100mg of ZnO is added, and the mixture is placed into an oven for reaction at 60 ℃ for 12h after being subjected to ultrasonic treatment for 10 min. And then centrifuging, washing and drying at 60 ℃ in vacuum to obtain the product ZnO @ ZIF-8.

And pyrolyzing the prepared ZnO @ ZIF-8 precursor in a tubular furnace under the nitrogen atmosphere. Keeping the gas flow rate at 300ml/min, raising the temperature to 900 ℃ at the temperature rise rate of 5 ℃/min, keeping the temperature at the target temperature for 1h, and then reducing the temperature for 60min to 300 ℃, wherein the obtained product is the HNC catalyst.

The constituent elements of the catalyst were C and N as determined by XPS, and the atomic ratio of nitrogen was 6.3%. The appearance of the nanospheres is hollow nanospheres when observed by a TEM.

From FIG. 2, it can be seen that the precursor has characteristic peaks of ZnO and ZIF-8.

It can be seen from fig. 6 that the HNC catalyst of comparative example 2 has better oxygen reduction activity than comparative example 1 in an oxygen-saturated 0.1M KOH aqueous solution. This is due to the increase in the proportion of mesopores. .

Example 1

Dissolving 1.878g of thioacetamide in 50ml of deionized water, adding 5g of ZnO, transferring to a reaction kettle, carrying out hydrothermal treatment at 90 ℃ for 1h, carrying out centrifugal separation, washing with deionized water for three times, and carrying out vacuum drying at 80 ℃ for 12h to obtain ZnO @ ZnS.

2-methylimidazole (0.04105g) is dissolved in 10ml of methanol, 100mg of ZnO @ ZnS is added, ultrasonic treatment is carried out for 10min, and then the mixture is put into an oven to react for 12h at 60 ℃. And then centrifuging, washing and drying at 60 ℃ in vacuum to obtain a product ZnO @ ZnS @ ZIF-8.

And pyrolyzing the prepared ZnO @ ZnS @ ZIF-8 precursor in a tubular furnace in a nitrogen atmosphere. Keeping the gas flow rate at 300ml/min, increasing the temperature to 900 ℃ at the temperature rise rate of 5 ℃/min, keeping the temperature at the target temperature for 1h, and then reducing the temperature for 60min to 300 ℃, wherein the obtained product is the HSNC catalyst.

It can be seen from fig. 3 that the XRD diffraction pattern of the catalyst obtained by heat treatment has a broad peak at 25 °, corresponding to the (002) crystal plane of graphitized carbon. The successful conversion of the precursor into a carbon material was demonstrated.

Fig. 4 shows that the nitrogen desorption curve of the catalyst in example 1 has a hysteresis loop with obvious mesoporous characteristics, which proves that the catalyst contains a large amount of mesoporous structures.

As can be seen from the pore size distribution diagram of fig. 5, the HSCN catalyst of example 1 contains micropores with a diameter of 1.3nm and mesopores with a diameter of 5 nm.

It can be seen from fig. 6 that the HSCN catalyst of example 1 has better oxygen reduction activity in 0.1M KOH aqueous solution saturated with oxygen than comparative examples 1 and 2. This benefits from rich mesostructure and S atom doping.

According to thermogravimetric testing, the ZnO mass ratio in the ZnO @ ZnS template is 16%.

The composition of the catalyst was determined by XPS to be C, N and S. The atomic ratio of N was 5.7% and the atomic ratio of S was 1.2%. The hollow structure is observed by TEM. According to BET tests, the proportion ratio of micropores to mesopores in the material is 61.7 percent and 38.3 percent.

Example 2

6g of elemental selenium and 4g of ZnO are mixed and heated at 800 ℃ for 15min to obtain ZnO @ ZnSe.

2-methylimidazole (0.04105g) is dissolved in 10ml of methanol, 100mg of ZnO @ ZnSe is added, ultrasonic treatment is carried out for 10min, and then the mixture is put into an oven to react for 12h at 60 ℃. And then obtaining a product ZnO @ ZnSe @ ZIF-8 after centrifugation, washing and drying at the temperature of 60 ℃ in vacuum.

And pyrolyzing the prepared ZnO @ ZnSe precursor in a tubular furnace in a nitrogen atmosphere. Keeping the gas flow rate at 300ml/min, increasing the temperature to 900 ℃ at the temperature rise rate of 5 ℃/min, keeping the temperature at the target temperature for 1h, and then reducing the temperature for 60min to 300 ℃, wherein the obtained product is the HSeNC catalyst.

According to thermogravimetric test, the ZnO mass ratio in the ZnO @ ZnSe template is 11%.

The composition of the catalyst was determined by XPS to be C, N and Se. The atomic ratio of N is 5.4%, and the atomic ratio of Se is 0.7%; the hollow structure is observed by TEM. According to BET tests, the proportion ratio of micropores to mesopores in the material is 58.5 percent and 41.5 percent.

It can be seen from fig. 6 that the HSeCN catalyst of example 2 has better oxygen reduction activity in 0.1M KOH aqueous solution saturated with oxygen than comparative examples 1 and 2. This benefits from rich mesoporous structure and Se atom doping.

Example 3

5.4g of zinc nitrate was weighed out and dissolved in 200ml of diethylene glycol, and stirred at 160 ℃ for 1 hour. Cooling to room temperature, centrifuging, washing, and vacuum drying at 60 ℃ for 8h to obtain the product, namely the ZnO nanosphere.

The composition of the catalyst was determined by XPS to be C, N and S. The atomic ratio of N was 4.6% and the atomic ratio of S was 1.1%. The hollow structure is observed by TEM. TEM observation shows that the morphology of a ZnO template is influenced by changing the type of zinc salt during ZnO preparation, and further the pore structure of the catalyst is influenced. According to BET tests, the proportion ratio of micropores to mesopores in the material is 66.3 percent and 33.7 percent.

Example 4

And pyrolyzing the prepared ZnO @ ZnS @ ZIF-8 precursor in a tubular furnace in a nitrogen atmosphere. Keeping the gas flow rate at 300ml/min, raising the temperature to 1000 ℃ at the temperature rise rate of 5 ℃/min, keeping the temperature at the target temperature for 1h, and then reducing the temperature for 60min to 300 ℃, wherein the obtained product is the HSNC catalyst.

When the heat treatment temperature was raised, part of the carbon skeleton collapsed at a high temperature and hetero atoms were lost, so that the doping amounts of N and S in the catalyst measured by XPS were reduced to 4.3% and 0.8%, respectively, as compared with example 1. Meanwhile, mesoporous channels are left at the positions where the components are lost, and compared with the material in the embodiment 1, the mesoporous ratio is increased to 44.7 percent, and the micropore ratio is 55.3 percent.

Example 5

Dissolving 1.878g of sodium sulfide in 50ml of deionized water, adding 5g of ZnO, transferring to a reaction kettle, carrying out hydrothermal treatment at 90 ℃ for 1h, carrying out centrifugal separation, washing with deionized water for three times, and carrying out vacuum drying at 80 ℃ for 12h to obtain ZnO @ ZnS.

From thermogravimetric tests, the mass ratio of ZnS in ZnO @ ZnS obtained by modifying ZnO with sodium sulfide is improved to 21% compared with that in example 1.

The composition of the catalyst was determined by XPS to be C, N and S. The atomic ratio of N is 5.2%, the S doping amount of the catalyst is increased due to the improvement of the ZnS mass ratio in the template, and the atomic ratio of S is 0.92%; the hollow structure is observed by TEM. According to BET tests, the proportion ratio of micropores to mesopores in the material is 52.3 percent and 47.7 percent.

Claims

1. A non-metallic catalyst characterized by: the carbon-doped hollow fiber is hollow particles, mainly comprises carbon, is doped with nitrogen and one or more than two of sulfur and selenium, and the atomic percent of nitrogen is 2-12%, preferably 6-9%; the atomic percentage of sulphur and/or selenium is between 0.5 and 6 percent, preferably between 1 and 3 percent; the mesoporous particle has a micropore and mesoporous hierarchical pore structure, wherein the micropore is positioned on the wall of the particle, the diameter of the micropore is 1-2nm, preferably 1.2-1.4nm, the hollow part of the particle is mesoporous, the diameter of the mesopore is 3-30nm, preferably 4-6nm, and the pore volume of the mesopore accounts for 10-60% of the total pore volume, preferably 25-40%.

2. The non-metallic catalyst of claim 1, wherein: the zinc oxide nano-particle is obtained by carbonizing a precursor, wherein the precursor is a core-shell structure in which the outer surface of a zinc oxide nano-particle is sequentially coated with a zinc sulfide layer and/or a zinc selenide layer and a zeolite imidazole ester framework (ZIF) layer, and the mass percentage of the zinc sulfide layer and/or the zinc selenide layer is 10-30%, preferably 15-25%. The mass percentage of the ZIF shell in the ZIF shell is 10-90%, preferably 40-50%.

3. The non-metallic catalyst of claim 1, wherein: the nitrogen exists in the form of one or more of pyridine nitrogen, pyrrole nitrogen, graphitized nitrogen and nitrogen oxide.

4. A method for preparing the non-metallic catalyst of any one of claims 1 to 3, wherein: comprises the following steps of (a) carrying out,

5. The method for preparing the non-metallic catalyst according to claim 4, wherein: the zinc salt in the step (1) is one or more than two of zinc nitrate, zinc acetate, zinc sulfate and zinc chloride; the heating temperature is 100-180 ℃, and the time is 0.5-2 h.

6. The method for preparing the non-metallic catalyst according to claim 4, wherein: in the vulcanization method in the step (2), the sulfur raw material is one or more than two of sodium sulfide or thioacetamide, and the method comprises the steps of dissolving the sulfur raw material in water, adding ZnO, and carrying out hydrothermal treatment at the temperature of 60-120 ℃ for 0.5-3 h; in the selenizing method, the selenium raw material is elemental selenium, and the method is to mix and heat the elemental selenium and ZnO at the temperature of 600-900 ℃ for 10-30 min.

7. The method for preparing the non-metallic catalyst according to claim 4, wherein: in the step (3), the solvent is one or more than two of methanol, ethanol, water and N, N-dimethylformamide; the imidazole ligand is one or more than two of imidazole, 2-methylimidazole and benzimidazole; the concentration of imidazole ligand is 0.01-1M, preferably 0.02-0.05M; the heating temperature is 40-80 ℃ and the time is 0.5-10 h.

8. The method for preparing the non-metallic catalyst according to claim 4, wherein: and (4) the inert atmosphere in the step (4) is one or a mixture of more than two of nitrogen and argon.

9. The method for preparing the non-metallic catalyst according to claim 4, wherein: the high-temperature carbonization treatment process in the step (4) is to heat the mixture from room temperature or drying humidity to 900-1100 ℃ at the heating rate of 5 ℃/min, keep the mixture for 1-3h, cool the mixture to 300 ℃ at the cooling rate of 1-10 ℃/min, and then naturally cool or naturally cool the mixture.

10. Use of a non-metallic catalyst according to any of claims 1 to 3, wherein: the catalyst can be used as an electrocatalyst for the oxygen reduction reaction of a cathode of an alkaline polymer electrolyte membrane fuel cell or a metal-air fuel cell.