CN113471452B - Multi-site composite nanotube for hydrogen and oxygen evolution reduction and preparation method and application thereof - Google Patents

Multi-site composite nanotube for hydrogen and oxygen evolution reduction and preparation method and application thereof Download PDF

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CN113471452B
CN113471452B CN202110738343.8A CN202110738343A CN113471452B CN 113471452 B CN113471452 B CN 113471452B CN 202110738343 A CN202110738343 A CN 202110738343A CN 113471452 B CN113471452 B CN 113471452B
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nanotube
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transition metal
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CN113471452A (en
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刘建国
丁睿
李佳
陈雅文
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Nanjing University
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/8647—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites
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    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
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    • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/90—Selection of catalytic material
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Abstract

The invention discloses a multi-site composite nanotube for hydrogen-oxygen evolution reduction and a preparation method and application thereof, wherein the nanotube takes nitrogen-doped porous carbon as a carbon source, melamine as a nitrogen source and transition metal particles as growth sites to form a bamboo joint-shaped structure in a composite manner; the surface and the interior of the nanotube are loaded with transition metal particles; the nanotube contains four-coordination metal-nitrogen sites with dispersed atoms, nitrogen doping sites which are not coordinated with metal and low-coordination metal-nitrogen sites positioned at the edge of the nanotube. According to the invention, the nanotube material obtained by calcining and pickling a nitrogen-doped porous carbon material obtained by pyrolyzing a zeolite imidazole framework structure and containing melamine and transition metal salt as a mixed precursor has a bamboo joint structure with a plurality of different types of active sites, has excellent hydrogen precipitation and oxygen reduction electrocatalytic activity and durability, can be applied to electrolytic water and zinc-air batteries, and has a wide application prospect.

Description

Multi-site composite nanotube for hydrogen and oxygen evolution reduction and preparation method and application thereof
Technical Field
The invention belongs to a nano material and a preparation method thereof, and particularly relates to a bamboo-shaped composite nanotube material containing multiple sites, and a preparation method and application thereof.
Background
In the electrocatalytic reaction, a Pt/C catalyst is used for both hydrogen evolution reaction and oxygen reduction reaction, however, the noble metal Pt is high in cost and low in reserves, and the related device is high in cost. Reducing Pt loading in both devices is therefore an important issue in the commercialization of renewable energy sources. Current research indicates that inexpensive transition metal-nitrogen doped carbon materials, such as Fe-NC/Co-NC materials, may be a promising alternative. The carbon nano tube is used as a material with good graphitization degree and excellent conductivity, and also has abundant capability of carrying active sites.
However, the current preparation method has high cost and poor stability, and is difficult to adapt to the molding preparation requirements of renewable energy sources. Zamani et al, which uses a commercial nanotube material to perform functionalization and then Polyaniline (PANI) coating as a precursor, need to perform stepwise calcination in an inert atmosphere and ammonia gas to obtain a composite catalytic material simultaneously containing nanotubes and graphene, have complicated steps and high cost, and are only reported to have oxygen reduction catalytic activity; zhang et al proposed that zeolite imidazolyl metal-organic framework materials (ZIF-8) with ultra-high specific surface area be mixed with commercial multi-walled carbon nanotubes for multiple calcination, and in the system, the nanotubes are considered to only mainly play a role in improving conductivity and have complex process steps and only have oxygen reduction catalytic activity; cheng et al proposed the use of dicyandiamide as a precursor to prepare nanotube catalysts containing a large number of transition metal monatomic sites, in which system the transition metal species are present only in a 4-coordinate form, and thus only Ni nanotubes were found to have carbon dioxide reduction catalytic activity; lu et al propose to mix dicyandiamide with ZIF and calcine to obtain atomically dispersed Ni-N site loaded nanotubes for CO2Reduction, the hydrogen evolution catalytic activity of the catalyst is low; in addition, many reports of preparing the metal-nitrogen-carbon catalyst by using carbon sources, nitrogen sources and metal source mixed calcination often only obtain a single catalytic active site mainly comprising Fe-N, and are limited to evaluating the catalytic performance in the oxygen reduction reaction. Therefore, how to design nanotube materials with composite structures and multiple functions becomes an urgent problem to be solved.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a bamboo-shaped composite nanotube material containing multiple sites and having the double functions of water electrolysis oxidation and reduction; the second purpose of the invention is to provide a method for preparing the composite nanotube, which is simple and low in cost; the third purpose of the invention is to provide the application of the composite nanotube material as an electrocatalyst.
The technical scheme is as follows: the composite nanotube containing multiple sites is characterized in that the nanotube takes nitrogen-doped porous carbon as a carbon source, melamine as a nitrogen source and transition metal particles as growth sites, and a bamboo joint-shaped structure is formed by compounding; the surface and the interior of the nanotube are loaded with transition metal particles; the nanotube contains four-coordination metal-nitrogen sites with dispersed atoms, nitrogen doping sites which are not coordinated with metal and low-coordination metal-nitrogen sites positioned at the edge of the nanotube.
Further, the transition metal comprises at least one of Fe, Co, Ni and Mn.
The invention also provides a preparation method of the composite nanotube containing multiple sites, which comprises the following steps:
(1) taking 2-methylimidazole and zinc nitrate hexahydrate as raw materials, obtaining a zeolite imidazole framework structure material by a water bath method, and performing high-temperature pyrolysis on the zeolite imidazole framework structure material to obtain a nitrogen-doped porous carbon carrier;
(2) adding a nitrogen-doped porous carbon carrier, a transition metal salt and melamine into a solvent, and performing magnetic stirring and mixing to obtain thick mixed precursor slurry;
(3) carrying out rotary evaporation on the mixed precursor slurry, and collecting and grinding the dried powder until a powder precursor is obtained;
(4) and placing the powder precursor into a tubular furnace, introducing inert atmosphere to calcine to obtain black carbon material powder, and then carrying out acid washing, suction filtration and drying to prepare the composite nanotube material.
Further, in the step (1), the molar ratio of the 2-methylimidazole to the zinc nitrate hexahydrate is 9: 1-7: 1; the high-temperature pyrolysis temperature is 900-1100 ℃, and the time is 1-2 h.
Further, in the step (2), the mass ratio of the transition metal salt to the melamine to the nitrogen-doped porous carbon carrier is 3-5: 32-64: 1; wherein the transition metal salt is at least one of chlorides, nitrates, acetates, carbonates, phosphates, sulfates, oxalates, citrates and acetylacetonato compounds of Fe, Co, Ni and Mn.
Further, in the step (2), the solvent is at least one of water, methanol, ethanol, N-propanol, acetone, ethylene glycol, isopropanol, butanol, dimethyl sulfoxide, and N, N-dimethylformamide; the stirring temperature is 20-30 ℃.
Further, in the step (3), the rotary evaporation temperature is 80-100 ℃, and the rotary evaporation operation time is 0.5-2 h.
Further, in the step (4), the inert gas is nitrogen or argon, the calcining temperature range is 800-1000 ℃, and the pyrolysis holding time range is 0.5-2 h.
Further, in the step (4), the type of the solution for acid washing is any one of dilute sulfuric acid, dilute hydrochloric acid, dilute perchloric acid and dilute nitric acid, the concentration is 0.1-1M, the acid washing temperature is 25-40 ℃, and the acid washing time is 1-6 days.
The invention further protects the application of the composite nanotube containing multiple sites as an electrocatalyst in electrolytic water or zinc-air batteries.
The composite nanotube material of the invention selects nitrogen-doped carbon derived from calcination of zeolite imidazole-based metal organic framework material with ultrahigh specific surface area as a carbon source, and can be mixed with melamine and transition metal salt as nitrogen sources, partially enriching transition metal and generating uniform transition metal nano particles in the pyrolysis process as the growth sites of the catalytic carbon tube, further leading the melamine to be in a bamboo joint shape when being used as a nitrogen source to grow the nano tube, therefore, a large number of nanotube edge sites are introduced, the low-coordination edge sites as one of a plurality of active sites of the composite nanotube have the rare high-efficiency hydrogen precipitation activity of the same system material, except the low-coordination transition metal-nitrogen sites, a plurality of transition metal nano particles coated by carbon shell layers and nitrogen-doped carbon sites are simultaneously arranged in the system, and four coordinated transition metal nitrogen sites, which have excellent catalytic activity for oxygen reduction reactions.
The forming principle of the invention is as follows: the nitrogen-doped carbon material derived from the unique zeolite imidazolyl framework has a rich microporous structure and an ultrahigh specific surface area, and can be uniformly adsorbed into micropores when being used as a carbon source to be mixed with melamine and transition metal salt serving as nitrogen sources. Upon pyrolysis calcination, the partially enriched transition metal salt will be reduced to uniform and fine transition metal nanoparticles early in the calcination pyrolysis. Therefore, the problems that the limited specific surface area and the nonuniform distribution of the transition metal salt precursor caused by the use of common carbon sources can be greatly reduced, the sizes of the nanotubes are different due to the nonuniform distribution of metal particles, and the amorphous carbon is easily formed can be solved. The uniform transition metal nanoparticles can catalyze the uniform growth of carbon nanotubes, which can adsorb carbonaceous particles, and carbon dissolved in the transition metal particles can diffuse to the bottom of the transition metal particles. Furthermore, the carbon graphite configuration is separated out from the bottom side of the transition metal particles, and when the number of graphite sheet layers is gradually increased, the transition metal particles and the graphite sheets are separated and move upwards due to interlayer stress concentration, so that a bamboo-shaped carbon nanotube structure is formed. Therefore, the generated bamboo joint structure edge is easy to enrich low-coordination metal-nitrogen sites so as to bring unique high hydrogen evolution activity. In addition, the nitrogen-rich melamine molecular nitrogen source can enable the wall of the grown bamboo-shaped nanotube to contain a large number of nitrogen doping sites, and the sites are coordinated with metal species which do not form particles to form four-coordinate metal-nitrogen sites or do not have a coordination effect with transition metals in a system. In addition, when the size of part of the transition metal nano-particles is larger, a core-shell structure coated by a plurality of carbon shell layers is formed, and a surface carbon layer of the core-shell structure is also rich in a large number of four-coordinate metal-nitrogen sites. These several sites have high catalytic activity in oxygen reduction catalysis. In addition, the conductivity of the system is improved by the bamboo-shaped nano tube, the electrocatalytic reaction is facilitated, and particles and various atomic-level dispersed sites existing in the system at the same time can be respectively applied to different electrocatalytic reactions. In addition, in the design of the composite structure, different catalytic sites which are close to each other, such as a transition metal simple substance partially wrapped in a carbon shell layer and metal-nitrogen in a surface shell layer can influence an electronic structure mutually, the center of a d-band is regulated and controlled, the adsorption energy of an original intermediate is optimized, a reaction potential barrier is reduced, and the intrinsic catalytic activity of the material is improved by a synergistic catalytic effect.
Has the beneficial effects that: compared with the prior art, the invention has the following remarkable advantages: the nanotube with the bamboo-shaped structure is prepared, and various different types of sites exist in a nanotube system, so that the nanotube has excellent hydrogen evolution and oxygen reduction electrocatalytic activity and durability, can be applied to electrolytic water and zinc-air batteries, and has wide application prospect; in the preparation process, precious metal raw materials are not used, the used precursors such as melamine and the like have low cost, the whole experimental device is simple, the whole steps are fewer, and the preparation scale and production can be enlarged.
Drawings
FIG. 1 is a scanning electron microscope and a transition metal element and nitrogen element energy spectrum picture of the bamboo-like composite nanotube obtained in examples 1-3;
FIG. 2 is a transmission electron microscope picture of the bamboo-like composite nanotube obtained in example 1-2;
FIG. 3 is a transmission electron microscope photograph of spherical aberration correction of the bamboo-like composite nanotubes obtained in example 1 and a spectrum image under the high magnification;
FIG. 4 shows the synchrotron radiation test results of the bamboo-like composite nanotubes obtained in example 1;
FIG. 5 shows the synchrotron radiation test results of the bamboo-like composite nanotubes obtained in example 2;
FIG. 6 shows the synchrotron radiation test results of the bamboo-like composite nanotubes obtained in example 3;
FIG. 7 is a scanning electron micrograph of the materials prepared in comparative examples 1 and 2;
FIG. 8 shows the results of characterization of hydrogen evolution activity of the bamboo-like composite nanotubes obtained in example 1 and amorphous carbon obtained in comparative examples 1 and 2;
FIG. 9 is the results of the characterization of the oxygen reduction catalytic activity and durability of the bamboo-like composite nanotubes obtained in example 1;
fig. 10 is the activity results in the zinc-air battery device with the bamboo-shaped composite nanotubes obtained in example 1;
FIG. 11 shows the results of a step current discharge durability test in a zinc-air battery device in which the bamboo-like composite nanotubes were obtained in example 1;
fig. 12 shows the result of the constant current discharge durability test in the zinc-air battery device obtained from the bamboo-shaped composite nanotube in example 1.
Detailed Description
The technical solution of the present invention is further described in detail with reference to the accompanying drawings and examples.
Example 1
(1) 6500mg of 2-methylimidazole is dissolved in 500mL of methanol to form a solution A, and 3000mg of zinc nitrate hexahydrate is dissolved in 500mL of methanol to form a solution B; mixing the solution A and the solution B, performing ultrasonic treatment for 5min, transferring the mixed solution into a clean beaker, performing magnetic stirring by using a magneton with the length of 20mm, and placing the beaker in a constant-temperature water bath kettle at 25 ℃ for reaction for 24 h; after the reaction, the stirring is stopped, the generated precipitate is settled at the bottom of the beaker, the supernatant is poured off, the precipitate containing a little supernatant is poured into a centrifuge tube, then methanol is added into the centrifuge tube, the centrifuge tube is centrifugally washed for three times by the methanol under the condition of 12000rpm for 5min, and the obtained precipitate is put into an air-blast drying oven to be dried overnight at 60 ℃. And pouring the dried white powder solid into a mortar for fully grinding, pouring the powder into a porcelain boat, placing the porcelain boat in a quartz tube of a tube furnace, carrying out heat treatment under the protection of nitrogen, heating to 950 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 1h, taking out after the temperature is reduced to room temperature, and fully grinding again to obtain the metal organic framework derived nitrogen-doped carbon carrier.
(2) 60mg of the nitrogen-doped carbon support obtained in the step (1), 2880mg of melamine powder and 113.6mg of anhydrous cobalt chloride were mixed in 100mL of ultrapure water, placed in a round-bottom flask, and thoroughly mixed in a water bath at 60 ℃ under reflux for 4 hours with vigorous stirring. After mixing sufficiently, a gray slurry was obtained, and then water in the slurry was removed by rotary evaporation at 80 ℃ for 1 hour using a rotary evaporation method to obtain a gray solid powder. And transferring the gray solid powder into a mortar for full grinding, pouring the gray fine powder into a porcelain boat, placing the porcelain boat in a quartz tube of a tube furnace, carrying out heat treatment under the protection of nitrogen, heating to 900 ℃ at a heating rate of 5 ℃/min, preserving heat for 1h, taking out after the temperature is reduced to room temperature, and fully grinding again to obtain the nanotube material before pickling.
(3) Weighing 100mg of the nanotube material obtained in the last step, preparing 0.5M dilute sulfuric acid, taking 200mL of the dilute sulfuric acid, placing the dilute sulfuric acid in a beaker, ultrasonically dispersing for 5min, adding magnetons with the diameter of 20mm, and violently stirring for acid cleaning. The acid wash step was continued for the entire 4 days at 25 ℃.
(4) And (3) carrying out suction filtration on the mixed solution after acid washing, washing with a large amount of ultrapure water, putting the product adhered to the filter paper together with the filter paper into a vacuum oven for drying overnight, and grinding the sample by using a mortar after drying to obtain the composite nanotube with the Co content of about 5 wt% in the final sample.
Example 2
(1) 6500mg of 2-methylimidazole is dissolved in 500mL of methanol to form a solution A, and 3000mg of zinc nitrate hexahydrate is dissolved in 500mL of methanol to form a solution B; mixing the solution A and the solution B, performing ultrasonic treatment for 5min, transferring the mixed solution into a clean beaker, performing magnetic stirring by using a magneton with the length of 20mm, and placing the beaker in a constant-temperature water bath kettle at 25 ℃ for reaction for 24 h; after the reaction, the stirring is stopped, the generated precipitate is settled at the bottom of the beaker, the supernatant is poured off, a little supernatant precipitate is poured into a centrifuge tube, then methanol is added into the centrifuge tube, the centrifuge tube is centrifugally washed for three times by methanol under the condition of 12000rpm for 5min, and the obtained precipitate is put into an air-blast drying oven to be dried overnight at 60 ℃. And pouring the dried white powder solid into a mortar for fully grinding, pouring the powder into a porcelain boat, placing the porcelain boat in a quartz tube of a tube furnace, carrying out heat treatment under the protection of nitrogen, heating to 950 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 1h, taking out after the temperature is reduced to room temperature, and fully grinding again to obtain the metal organic framework derived nitrogen-doped carbon material.
(2) 60mg of the nitrogen-doped carbon support obtained in the step (1), 2880mg of melamine powder and 115mg of anhydrous nickel chloride were mixed in 100mL of ultrapure water, placed in a round-bottom flask, and thoroughly mixed in a water bath at 60 ℃ under reflux for 4 hours while keeping vigorous stirring. After mixing sufficiently, a gray slurry is obtained, and then water in the slurry is removed by rotary evaporation for 1h at the temperature of 80 ℃ by using a rotary evaporation method, so that a gray solid powder is obtained. And transferring the gray solid powder into a mortar for full grinding, pouring the gray fine powder into a porcelain boat, placing the porcelain boat in a quartz tube of a tube furnace, carrying out heat treatment under the protection of nitrogen, heating to 900 ℃ at a heating rate of 5 ℃/min, preserving heat for 1h, taking out after the temperature is reduced to room temperature, and fully grinding again to obtain the nanotube material before pickling.
(3) Weighing 100mg of the nanotube material obtained in the last step, preparing 0.5M dilute sulfuric acid, taking 200mL of the dilute sulfuric acid, placing the dilute sulfuric acid in a beaker, ultrasonically dispersing for 5min, adding magnetons with the diameter of 20mm, and violently stirring for acid cleaning. The acid wash step was continued at 25 ℃ for the entire 4 days.
(4) And (3) carrying out suction filtration on the mixed solution after acid washing, washing by using a large amount of ultrapure water, putting the product adhered to the filter paper together with the filter paper into a vacuum oven for drying overnight, and grinding the sample by using a mortar after drying to obtain the composite nanotube with the Ni content of about 10 wt% in the final sample.
Example 3
(1) 6500mg of 2-methylimidazole is dissolved in 500mL of methanol to form a solution A, and 3000mg of zinc nitrate hexahydrate is dissolved in 500mL of methanol to form a solution B; mixing the solution A and the solution B, performing ultrasonic treatment for 5min, transferring the mixed solution into a clean beaker, performing magnetic stirring by using a magneton with the length of 20mm, and placing the beaker in a constant-temperature water bath kettle at 25 ℃ for reaction for 24 h; after the reaction, the stirring is stopped, the generated precipitate is settled at the bottom of the beaker, the supernatant is poured off, the precipitate containing a little supernatant is poured into a centrifuge tube, then methanol is added into the centrifuge tube, the centrifuge tube is centrifugally washed for three times by the methanol under the condition of 12000rpm for 5min, and the obtained precipitate is put into an air-blast drying oven to be dried overnight at 60 ℃. And pouring the dried white powder solid into a mortar for fully grinding, pouring the powder into a porcelain boat, placing the porcelain boat in a quartz tube of a tube furnace, carrying out heat treatment under the protection of nitrogen, heating to 950 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 1h, taking out after the temperature is reduced to room temperature, and fully grinding again to obtain the metal organic framework derived nitrogen-doped carbon carrier.
(2) 60mg of the nitrogen-doped carbon support obtained in the step (1), 2880mg of melamine powder and 112mg of anhydrous ferric chloride were mixed in 100mL of ultrapure water, placed in a round-bottom flask, and thoroughly mixed in a water bath at 60 ℃ under reflux for 4 hours while keeping vigorous stirring. After mixing sufficiently, a gray slurry was obtained, and then water in the slurry was removed by rotary evaporation at 80 ℃ for 1 hour using a rotary evaporation method to obtain a gray solid powder. And transferring the gray solid powder into a mortar for full grinding, pouring the gray fine powder into a porcelain boat, placing the porcelain boat in a quartz tube of a tube furnace, carrying out heat treatment under the protection of nitrogen, heating to 900 ℃ at a heating rate of 5 ℃/min, preserving heat for 1h, taking out after the temperature is reduced to room temperature, and fully grinding again to obtain the nanotube material before pickling.
(3) Weighing 100mg of the nanotube material obtained in the last step, preparing 0.5M dilute sulfuric acid, taking 200mL of the dilute sulfuric acid, placing the dilute sulfuric acid in a beaker, ultrasonically dispersing for 5min, adding magnetons with the diameter of 20mm, and violently stirring for acid cleaning. The acid wash step was continued for the entire 4 days at 25 ℃.
(4) And (3) carrying out suction filtration on the mixed solution after acid washing, washing by using a large amount of ultrapure water, putting the product adhered to the filter paper together with the filter paper into a vacuum oven for drying overnight, and grinding the sample by using a mortar after drying to obtain the composite nanotube with the Fe content of about 15 wt% in the final sample.
In fig. 1, a, b, and c show the scanning electron microscope morphology pictures of the bamboo-like composite nanotube materials obtained in examples 1, 2, and 3, respectively. As can be seen, the system is a nanotube (varying with the transition metal species) with a diameter of about 30 to 100 nm. Scanning the distribution of transition metal elements Fe, Co and Ni and the distribution of nitrogen elements by an energy spectrum can see that a small amount of transition metal particles exist simultaneously and transition metal signals which do not exist in the form of particles are uniformly distributed on the nanotube in the system. The transition metal particles and nitrogen-doped carbon sites are proved to be present in the system. Further, transmission electron microscopy is performed through fig. 2 for characterization, a and b are bamboo-like nanotubes corresponding to the morphologies of the bamboo-like composite nanotube materials obtained in examples 1 and 2, respectively, and transition metal particles coated by a carbon shell exist in the nanotubes, which is consistent with the scanning electron microscopy shooting result in fig. 1. Further, a subatomic level observation of the bamboo-like composite nanotubes obtained in example 1 was performed by using a spherical aberration correction transmission electron microscope with subatomic resolution, as shown in fig. 3, it can be seen that a large number of atomically dispersed Co atoms were present at the bamboo joint and on the flat nanotube wall, and the energy spectrum scanning result shown shows that the Co element and the N element were uniformly distributed in the region where no metal particles were present in the material. Thus demonstrating the presence of Co-NC atomic sites in the system.
By synchrotron radiation testing, as shown in fig. 4-6, the samples can be analyzed for the presence of metallic elements.
Referring to fig. 4, in a, the result shown in the near-edge absorption spectrum indicates that the valence state of Co in the bamboo-shaped composite nanotube obtained in example 1 is slightly higher than the valence state of Co in the simple Co substance, and has a certain positive valence, which indicates that Co species coordinated with N exists in the system, and is consistent with the aforementioned characterization result. In addition, the fitting of b and c can find that in the bamboo-shaped composite nanotube obtained in example 1, not only a peak corresponding to a Co-Co bond simple substance exists, but also a peak coordinated by Co-N and smaller than 2 angstroms exists, which proves that two sites exist simultaneously in the system, and the results are consistent with the results of the previous figures 1 to 3.
Referring to fig. 5 and fig. 6, the same characterization analysis is performed on the bamboo-shaped composite nanotubes obtained in examples 2 and 3, respectively, and it is further confirmed that two catalytic active sites, i.e., sites coordinated at atomic level and transition metal simple substance particles, exist in the bamboo-shaped composite nanotubes at the same time. By performing transformation fitting on the synchrotron radiation absorption spectrum, it can be found that in the nanotube catalyst prepared by the method, a considerable amount of metal-nitrogen species exist in a low coordination form with a coordination number less than 2, and the metal-nitrogen species are different from the four-coordination metal-nitrogen sites commonly reported at present, which shows that the bamboo-shaped coincidence nanotube prepared by the strategy also has unique edge coordination metal-nitrogen sites. This is consistent with the observation of atomically dispersed edge metal atoms at the bamboo junctions in the bamboo composite nanotubes obtained in example 1, as characterized by the spherical aberration corrected transmission electron microscope in FIG. 3.
Example 4
The specific preparation method is the same as that of example 1, except that: in the step (1), the molar ratio of the 2-methylimidazole to the zinc nitrate hexahydrate is 9: 1, the pyrolysis temperature is 900 ℃, and the heat preservation time is 2 h; in the step (2), the transition metal salt adopts anhydrous manganese chloride, and the mass ratio of the transition metal salt to the nitrogen-doped carbon carrier is 3: 1, the mass ratio of melamine to nitrogen-doped carbon carrier is 32: 1, adopting N, N-dimethylformamide as a solvent; in the step (3), the rotary evaporation operation temperature is 100 ℃, and the time is 2 hours; in the step (4), the pyrolysis temperature is 800 ℃, the heat preservation time is 2 hours, hydrochloric acid is adopted for pickling, the concentration is 0.1M, the volume is 200mL, and the pickling temperature is 25 ℃; the acid washing time was 6 days.
Finally, the bamboo-shaped composite nano-tube with the edge, the four-coordination manganese-nitrogen single-atom site, the manganese nano-particles and the nitrogen-doped site which is not coordinated with the metal is prepared.
Example 5
The specific preparation method is the same as that of example 2, except that: in the step (1), the molar ratio of the 2-methylimidazole to the zinc nitrate hexahydrate is 7: 1, the pyrolysis temperature is 1100 ℃, and the heat preservation time is 1 h; the mass ratio of the transition metal salt to the nitrogen-doped carbon carrier in the step (2) is 5: 1, the mass ratio of melamine to nitrogen-doped carbon carrier is 64: 1, using acetone as a solvent; in the step (3), the rotary evaporation operation temperature is 80 ℃, and the time is 0.5 h; the pyrolysis temperature of the step (4) is 1000 ℃, the heat preservation time is 0.5h, nitric acid is adopted for pickling, the concentration is 1M, the volume is 200mL, and the pickling temperature is 40 ℃; the acid washing time was 1 day.
Finally, the bamboo-shaped composite nano-tube with the edge, the four-coordination nickel-nitrogen single-atom site, the nickel nano-particles and the nitrogen-doped site which is not coordinated with the metal is prepared.
Example 6
The specific preparation method is the same as example 3, except that: in the step (1), the molar ratio of the 2-methylimidazole to the zinc nitrate hexahydrate is 9: 1, the pyrolysis temperature is 1000 ℃, and the heat preservation time is 1.5 h; the mass ratio of the transition metal salt to the nitrogen-doped carbon carrier in the step (2) is 3: 1, the mass ratio of melamine to nitrogen-doped carbon carrier is 64: 1, the solvent adopts ethylene glycol; in the step (3), the rotary evaporation operation temperature is 100 ℃, and the time is 1 h; the pyrolysis temperature of the step (4) is 1000 ℃, the heat preservation time is 2 hours, perchloric acid is adopted for acid washing, the concentration is 1M, the volume is 200mL, and the acid washing temperature is 25 ℃; the acid washing time was 6 days.
Finally preparing the bamboo-shaped composite nanotube with the edge, four coordinated iron-nitrogen single atom sites, iron nano particles and nitrogen doping sites which are not coordinated with metal.
Comparative example 1
(1) 60mg of EC600 conductive carbon black powder, 2880mg of melamine and 113.6mg of anhydrous cobalt chloride were mixed in 100ml of ultrapure water, placed in a round-bottomed flask, and thoroughly mixed in a water bath at 60 ℃ under reflux with vigorous stirring for 4 hours. After mixing thoroughly, a grey slurry was obtained, and then water was removed from the slurry at 80 ℃ by rotary evaporation to obtain a grey solid powder. And transferring the gray solid powder into a mortar for full grinding, pouring the fine gray powder into a porcelain boat, placing the porcelain boat in a quartz tube of a tube furnace, carrying out heat treatment under the protection of nitrogen, heating to 900 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 1h, taking out after the temperature is reduced to room temperature, and fully grinding again to obtain the nanotube material before pickling.
(2) Weighing 100mg of the nanotube material obtained in the last step, preparing 0.5M dilute sulfuric acid, taking 200mL of the dilute sulfuric acid, placing the dilute sulfuric acid in a beaker, ultrasonically dispersing for 5min, adding magnetons with the diameter of 20mm, and violently stirring for acid cleaning. The acid wash step lasted for the entire 4 days at room temperature.
(3) And (3) carrying out suction filtration on the mixed solution after acid washing, washing by using a large amount of ultrapure water, putting the product adhered to the filter paper together with the filter paper into a vacuum oven for drying overnight, and grinding the sample by using a mortar after drying to obtain the amorphous carbon material with the Co content of about 7 wt% in the final sample.
Comparative example 2
(1) 1g of urea and 500mg of EC600 conductive carbon black powder are mixed, uniformly ground in a mortar for 1 hour to obtain fine powder, and pyrolyzed in a tube furnace at 900 ℃ for 1 hour to obtain nitrogen-doped carbon powder.
(2) 60mg of the nitrogen-doped carbon powder described in the above step (1), 2880mg of melamine and 113.6mg of anhydrous cobalt chloride were mixed in 100ml of ultrapure water, placed in a round-bottom flask, and thoroughly mixed in a water bath at 60 ℃ under reflux for 4 hours while keeping vigorous stirring. After mixing thoroughly, a grey slurry was obtained, and then water was removed from the slurry at 80 ℃ by rotary evaporation to obtain a grey solid powder. And transferring the gray solid powder into a mortar for full grinding, pouring the gray fine powder into a porcelain boat, placing the porcelain boat in a quartz tube of a tube furnace, carrying out heat treatment under the protection of nitrogen, heating to 900 ℃ at a heating rate of 5 ℃/min, preserving heat for 1h, taking out after the temperature is reduced to room temperature, and fully grinding again to obtain the nanotube material before pickling.
(3) Weighing 100mg of the nanotube material obtained in the last step, preparing 0.5M dilute sulfuric acid, taking 200mL of the dilute sulfuric acid, placing the dilute sulfuric acid in a beaker, ultrasonically dispersing for 5min, adding magnetons with the diameter of 20mm, and violently stirring for acid cleaning. The acid wash step lasted for the entire 4 days at room temperature.
(4) And (3) carrying out suction filtration on the mixed solution after acid washing, washing with a large amount of ultrapure water, putting the product adhered to the filter paper together with the filter paper into a vacuum oven for drying overnight, and grinding the sample by using a mortar after drying to obtain the amorphous carbon material with the Co content of about 5 wt% in the final sample.
The key point of the bamboo-shaped composite nanotube material is the selection of a carbon source in a precursor. In fig. 7, a and b show scanning electron micrographs of the morphology of samples finally obtained in comparative examples 1 and 2, respectively, when a common EC600 conductive carbon black material and a nitrogen-doped EC600 material are used instead of metal organic framework-derived nitrogen-doped carbon as precursors. As can be seen from the figure, when two common carbon sources, namely, a nitrogen-doped carbon material containing no nitrogen or a nitrogen-doped carbon material calcined by mixing urea and conductive carbon black, are used, the uniform bamboo-like nanotube structure obtained in the case of using the nitrogen-doped carbon material derived from the metal organic framework as the carbon source in example 1 cannot be obtained. The final materials obtained in comparative examples 1 and 2 are more prone to amorphous carbon, and a few nanotubes do not have a bamboo-like structure, and therefore lack low-coordination metal-nitrogen active sites on the edges. This is because the conventional conductive carbon black and the nitrogen-doped EC600 with a low specific surface area cannot locally enrich the transition metal ions, and nanoparticles for catalyzing the growth of the bamboo-like nanotubes are uniformly generated in the pyrolysis process. Evaluation of electrochemical activity of the prepared nanotube material, as shown in FIG. 8, the bamboo-like composite nanotubes obtained in example 1 have good catalytic activity for hydrogen evolution in an acidic medium at 10mA cm-2The overpotential is 82 mV. Whereas the amorphous carbon obtained in comparative examples 1 and 2 was overpowered under the same test conditionsThe bit exceeds 150mV, which proves that the edge low coordination metal-nitrogen site with unique high hydrogen precipitation activity of the bamboo-shaped composite nanotube can be obtained only by using metal organic framework derived nitrogen-doped carbon as a precursor carbon source.
Application of multifunctional electrocatalyst in water electrolysis and zinc-air battery
The bamboo-like composite nanotube obtained in example 1 has, in addition to the low coordination metal-nitrogen-hydrogen evolution active sites located at the bamboo joint edges, carbon shell-coated nanoparticles, nitrogen-doped carbon sites and atomically dispersed Co-N4 sites present on the nanotube wall as observed in the previous characterization. The sites also have excellent catalytic activity in oxygen reduction, so that the bamboo-shaped composite nanotube has multiple electrocatalytic functions. As shown in fig. 9, the half-wave potential of the bamboo-like composite nanotubes obtained in example 1 was only 4mV lower than that of the commercial Pt/C catalyst in 1M KOH solution saturated with oxygen. But the durability is more excellent, after 10k circle potentiodynamic durability test, the ORR catalytic performance of the commercial Pt/C noble metal catalyst is reduced sharply, and the bamboo-shaped composite nanotube obtained in the example 1 has almost no attenuation. The composite nanotube prepared by the invention has excellent application potential in water electrolysis devices.
The bamboo-like composite nanotube obtained in the embodiment 1 also has an application prospect in a zinc-air battery. As shown in FIG. 10, in the zinc-air battery, the bamboo-shaped composite nanotube obtained in example 1 is used as a cathode catalyst, a zinc plate is used as an anode, and the peak power density of the assembled zinc-air battery can reach 129mW cm-2However, commercial Pt/C as cathode has a peak power density of only 107mW cm at much higher cost-2. In addition, as shown in FIG. 11, in different steps (10mA cm)-2；20mA cm-2；50mA cm-2) Constant current discharge and long-time constant current discharge as shown in fig. 12, the zinc-air battery assembled with commercial Pt/C as cathode catalyst was inferior in performance and durability to the bamboo-like composite nanotubes obtained in example 1.

Claims (8)

1. A preparation method of a multi-site composite nanotube for hydrogen and oxygen evolution reduction is characterized by comprising the following steps: the nanotube is compounded into a bamboo joint-shaped structure by taking nitrogen-doped porous carbon as a carbon source, melamine as a nitrogen source and transition metal particles as growth sites; the surface and the interior of the nanotube are loaded with transition metal particles; the nanotube contains four-coordination metal-nitrogen sites with dispersed atoms, nitrogen doping sites which are not coordinated with metals and low-coordination metal-nitrogen sites positioned at the edge of the nanotube, wherein the transition metal comprises at least one of Fe, Co, Ni and Mn, and the preparation method comprises the following steps:
(1) taking 2-methylimidazole and zinc nitrate hexahydrate as raw materials, obtaining a zeolite imidazole framework structure material by a water bath method, and performing high-temperature pyrolysis on the zeolite imidazole framework structure material to obtain a nitrogen-doped porous carbon carrier;
(2) adding a nitrogen-doped porous carbon carrier, transition metal salt and melamine into a solvent, and performing magnetic stirring and mixing to obtain thick mixed precursor slurry;
(3) carrying out rotary evaporation on the mixed precursor slurry, and collecting and grinding the dried powder until a powder precursor is obtained;
(4) and placing the powder precursor into a tubular furnace, introducing inert atmosphere to calcine to obtain black carbon material powder, and then carrying out acid washing, suction filtration and drying to prepare the composite nanotube material.
2. The method for producing a multi-site composite nanotube for oxyhydrogen reduction according to claim 1, characterized in that: in the step (1), the molar ratio of 2-methylimidazole to zinc nitrate hexahydrate is 9: 1-7: 1; the temperature of the high-temperature pyrolysis is 900-1100 ℃, and the time is 1-2 h.
3. The method for producing a multi-site composite nanotube for oxyhydrogen reduction according to claim 1, characterized in that: in the step (2), the mass ratio of the transition metal salt to the melamine to the nitrogen-doped porous carbon carrier is 3-5: 32-64: 1; wherein the transition metal salt is at least one of chlorides, nitrates, acetates, carbonates, phosphates, sulfates, oxalates, citrates and acetylacetonato compounds of Fe, Co, Ni and Mn.
4. The method for producing a multi-site composite nanotube for oxyhydrogen reduction according to claim 1, characterized in that: in the step (2), the solvent is at least one of ultrapure water, methanol, ethanol, N-propanol, acetone, ethylene glycol, isopropanol, butanol, dimethyl sulfoxide and N, N-dimethylformamide; the stirring temperature is 20-30 ℃.
5. The method for producing a multi-site composite nanotube for oxyhydrogen reduction according to claim 1, characterized in that: in the step (3), the rotary evaporation temperature is 80-100 ℃, and the rotary evaporation operation time is 0.5-2 h.
6. The method for producing a multi-site composite nanotube for oxyhydrogen reduction according to claim 1, characterized in that: in the step (4), the inert atmosphere is nitrogen or argon, the calcining temperature ranges from 800 ℃ to 1000 ℃, and the pyrolysis holding time ranges from 0.5h to 2 h.
7. The method for producing a multi-site composite nanotube for oxyhydrogen reduction according to claim 1, characterized in that: in the step (4), the type of the solution for acid washing is any one of dilute sulfuric acid, dilute hydrochloric acid, dilute perchloric acid and dilute nitric acid, the concentration is 0.1-1M, the acid washing temperature is 25-40 ℃, and the acid washing time is 1-6 days.
8. Use of the multi-site composite nanotube for oxyhydrogen evolution reduction prepared by the preparation method according to claim 1 as an electrocatalyst in electrolytic water or zinc-air batteries.
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