CN111569929A - Co-MOF derived cobalt/nitrogen/carbon composite material and preparation method thereof - Google Patents
Co-MOF derived cobalt/nitrogen/carbon composite material and preparation method thereof Download PDFInfo
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 118
- 239000002131 composite material Substances 0.000 title claims abstract description 63
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 61
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 53
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 49
- 229910017052 cobalt Inorganic materials 0.000 title claims abstract description 45
- 239000010941 cobalt Substances 0.000 title claims abstract description 45
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 title claims abstract description 45
- 238000002360 preparation method Methods 0.000 title claims abstract description 20
- 239000012921 cobalt-based metal-organic framework Substances 0.000 title claims abstract 14
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 37
- 239000001301 oxygen Substances 0.000 claims abstract description 37
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 37
- 239000002243 precursor Substances 0.000 claims abstract description 21
- 239000000725 suspension Substances 0.000 claims abstract description 14
- 238000004519 manufacturing process Methods 0.000 claims abstract description 12
- 238000005406 washing Methods 0.000 claims abstract description 11
- 238000001035 drying Methods 0.000 claims abstract description 6
- 238000002156 mixing Methods 0.000 claims abstract description 4
- 238000002955 isolation Methods 0.000 claims abstract description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 36
- 239000000243 solution Substances 0.000 claims description 33
- 229920002873 Polyethylenimine Polymers 0.000 claims description 32
- 238000002347 injection Methods 0.000 claims description 22
- 239000007924 injection Substances 0.000 claims description 22
- 238000000034 method Methods 0.000 claims description 19
- YSWBFLWKAIRHEI-UHFFFAOYSA-N 4,5-dimethyl-1h-imidazole Chemical compound CC=1N=CNC=1C YSWBFLWKAIRHEI-UHFFFAOYSA-N 0.000 claims description 11
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 10
- QGUAJWGNOXCYJF-UHFFFAOYSA-N cobalt dinitrate hexahydrate Chemical compound O.O.O.O.O.O.[Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O QGUAJWGNOXCYJF-UHFFFAOYSA-N 0.000 claims description 9
- 239000007788 liquid Substances 0.000 claims description 9
- 238000000520 microinjection Methods 0.000 claims description 8
- 238000006243 chemical reaction Methods 0.000 claims description 6
- 238000001291 vacuum drying Methods 0.000 claims description 5
- 230000009467 reduction Effects 0.000 abstract description 28
- 230000003197 catalytic effect Effects 0.000 abstract description 7
- 239000007772 electrode material Substances 0.000 abstract description 4
- 230000007547 defect Effects 0.000 abstract description 2
- 238000006722 reduction reaction Methods 0.000 description 28
- 239000003054 catalyst Substances 0.000 description 22
- 239000000463 material Substances 0.000 description 12
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 8
- 238000003763 carbonization Methods 0.000 description 6
- 239000012621 metal-organic framework Substances 0.000 description 6
- 238000012360 testing method Methods 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 238000000840 electrochemical analysis Methods 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 229910002804 graphite Inorganic materials 0.000 description 4
- 239000010439 graphite Substances 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 238000012986 modification Methods 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 4
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 239000000446 fuel Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 238000001000 micrograph Methods 0.000 description 3
- 238000011056 performance test Methods 0.000 description 3
- 229910052697 platinum Inorganic materials 0.000 description 3
- 238000000197 pyrolysis Methods 0.000 description 3
- 238000004832 voltammetry Methods 0.000 description 3
- 230000010757 Reduction Activity Effects 0.000 description 2
- 238000000026 X-ray photoelectron spectrum Methods 0.000 description 2
- 230000002776 aggregation Effects 0.000 description 2
- 238000004220 aggregation Methods 0.000 description 2
- AAMATCKFMHVIDO-UHFFFAOYSA-N azane;1h-pyrrole Chemical compound N.C=1C=CNC=1 AAMATCKFMHVIDO-UHFFFAOYSA-N 0.000 description 2
- YDVGDXLABZAVCP-UHFFFAOYSA-N azanylidynecobalt Chemical compound [N].[Co] YDVGDXLABZAVCP-UHFFFAOYSA-N 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 239000008367 deionised water Substances 0.000 description 2
- 229910021641 deionized water Inorganic materials 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 2
- 239000013110 organic ligand Substances 0.000 description 2
- 230000000704 physical effect Effects 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000004062 sedimentation Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 239000012300 argon atmosphere Substances 0.000 description 1
- DLGYNVMUCSTYDQ-UHFFFAOYSA-N azane;pyridine Chemical compound N.C1=CC=NC=C1 DLGYNVMUCSTYDQ-UHFFFAOYSA-N 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 150000001868 cobalt Chemical class 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000010411 electrocatalyst Substances 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 239000002082 metal nanoparticle Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000002105 nanoparticle Substances 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 125000004433 nitrogen atom Chemical group N* 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003623 transition metal compounds Chemical class 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
- 229910021642 ultra pure water Inorganic materials 0.000 description 1
- 239000012498 ultrapure water Substances 0.000 description 1
- 238000001132 ultrasonic dispersion Methods 0.000 description 1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/24—Nitrogen compounds
-
- B01J35/33—
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/9041—Metals or alloys
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/9075—Catalytic material supported on carriers, e.g. powder carriers
- H01M4/9083—Catalytic material supported on carriers, e.g. powder carriers on carbon or graphite
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Abstract
The invention relates to a Co-MOF derived cobalt/nitrogen/carbon composite material and a preparation method thereof. A method of making a Co-MOF derived cobalt/nitrogen/carbon composite comprising: (1) preparing a precursor solution A, B; (2) preparation of Co-MOF derived cobalt/nitrogen/carbon composite: mixing the precursor solution A, B to prepare a suspension, centrifuging, washing, and drying in vacuum to obtain a Co-MOF composite material; treating the Co-MOF composite material at the temperature of 900 ℃ under the conditions of oxygen isolation and 800-. The Co-MOF derived cobalt/nitrogen/carbon composite material and the preparation method thereof overcome the defect of low catalytic efficiency of the traditional oxygen reduction electrode material, and prepare the oxygen reduction electrode material with good conductivity and high catalytic efficiency.
Description
Technical Field
The invention particularly relates to a Co-MOF derived cobalt/nitrogen/carbon composite material and a preparation method thereof.
Background
Fuel cells, as a device for converting chemical energy into electrical energy, have the characteristics of high density and environmental friendliness. It is well known that the slow cathodic oxygen reduction reaction is a critical reaction for fuel cells. Platinum-based material catalysts are the most effective catalysts for catalyzing oxygen reduction reactions. However, the platinum-based material has problems of rare earth shell, high cost, poor stability, poor methanol resistance and the like, and thus the large-scale application of the fuel cell is severely restricted. Therefore, the search for a high-activity, stable and low-cost oxygen reduction catalyst instead of the platinum-based catalyst has been a hot research topic in this field.
Transition metal compounds and nitrogen-doped metal carbon materials are always the research hotspots of people. Wherein, metal and nitrogen atom can induce the uneven distribution of electric charge, thereby improving the adsorption and reduction of oxygen and further improving the catalytic performance of oxygen reduction. Of the many transition metals, metallic cobalt nitrogen doped carbon catalysts are considered to be the most promising high oxygen reduction activity platinum-free carbon catalysts. The metal organic framework is chosen as a precursor for the preparation of the catalyst because of its particular structure. This is because in the metal organic framework material, the nitrogen-containing organic ligand not only serves as a carbon source but also can serve as a nitrogen source, and after high-temperature carbonization, metal ions of the nitrogen-containing organic ligand are converted into metal oxides, metal nitrides or metal nanoparticles to synergistically improve the catalytic performance.
However, the inevitable aggregation thereof during pyrolysis at high temperatures may result in undesirable physical properties of the cobalt/nitrogen/carbon composite. For example, as the pyrolysis temperature is increased, the metal-organic framework collapses, so that the specific surface area, pore volume and pore diameter of the material are changed, and the electrocatalytic oxygen reduction performance of the material is negatively influenced. Moreover, the preparation process is complicated and time-consuming.
In view of the above, the invention provides a novel preparation method of a Co-MOF derived cobalt/nitrogen/carbon composite material, so that the Co-MOF derived cobalt/nitrogen/carbon composite material can still maintain good results and satisfactory physical properties in a high-temperature treatment process.
Disclosure of Invention
The invention aims to provide a preparation method of a Co-MOF derived cobalt/nitrogen/carbon composite material, which has the advantages of short preparation period and low cost and overcomes the defect of low catalytic efficiency of the traditional oxygen reduction electrode material.
In order to realize the purpose, the adopted technical scheme is as follows:
a method of making a Co-MOF derived cobalt/nitrogen/carbon composite comprising the steps of:
(1) preparing a precursor solution:
dissolving cobalt nitrate hexahydrate in methanol to obtain a precursor solution A;
dissolving polyethyleneimine and dimethyl imidazole in a methanol solution to obtain a precursor solution B;
(2) preparation of Co-MOF derived cobalt/nitrogen/carbon composite:
sucking the precursor liquid A, B with an injector respectively in equal amount, and placing on a micro-injection pump; under a certain injection speed, quickly pushing the two solutions into a reaction mold for quick mixing to obtain a suspension;
after the suspension is centrifugally washed, vacuum drying is carried out to obtain a Co-MOF composite material;
and (2) treating the Co-MOF composite material at the temperature of 900 ℃ under the conditions of oxygen isolation and 800-.
Further, in the step (1), the mass ratio of the cobalt nitrate hexahydrate, the polyethyleneimine and the dimethylimidazole in the precursor liquid A, B is 0.736:0.306: 1.624.
Further, in the step (2), the injection speed is 30-100 ml/min.
Still further, in the step (2), the injection speed is 90 ml/min.
Further, in the step (2), the centrifugal washing rotation speed of the suspension is 7000-8000 r/min;
the centrifugal washing adopts methanol solution.
Further, in the step (2), the Co-MOF composite material is treated for 2 hours at 900 ℃.
Still further, in the step (2), the Co-MOF composite material is treated at 900 ℃.
Further, after the washing to be neutral, the mixture is dried for 24 hours at 80 ℃.
Further, the concentration of the dilute sulfuric acid is 0.5 mol/L.
The invention also aims to provide a Co-MOF derived cobalt/nitrogen/carbon composite material which is obtained by adopting the preparation method and is an oxygen reduction electrode material with good conductivity and high catalytic efficiency.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention provides a novel Co-MOF (cobalt-metal organic framework) -derived cobalt/nitrogen/carbon composite material and a preparation method thereof.
2. The invention adopts instantaneous nanometer sedimentation technology (FNP), has simple and convenient method, low cost and short time, and can enlarge the production scale of materials.
3. The invention adopts Polyethyleneimine (PEI), avoids excessive collapse of Co-MOF, improves the specific surface area of the product, and simultaneously improves the content of nitrogen, so that the Co-MOF derived cobalt/nitrogen/carbon composite material has excellent oxygen reduction electrocatalytic performance.
Drawings
FIG. 1 is a scanning electron microscope image of an oxygen reduction catalyst prepared in example 1 of the present invention;
FIG. 2 is an X-ray diffraction spectrum of an oxygen-reducing catalyst prepared in example 1 of the present invention;
FIG. 3 shows the oxygen reduction electrocatalytic performance of the catalyst prepared in example 1 of the present invention;
FIG. 4 is a scanning electron microscope image of an oxygen reduction catalyst prepared in example 2 of the present invention;
FIG. 5 is an X-ray diffraction spectrum of an oxygen-reducing catalyst prepared in example 2 of the present invention;
FIG. 6 shows the oxygen reduction electrocatalytic performance of the catalyst prepared in example 2 of the present invention;
FIG. 7 is a scanning electron microscope image of an oxygen reduction catalyst prepared in example 3 of the present invention;
FIG. 8 is an X-ray diffraction spectrum of an oxygen-reducing catalyst prepared in example 3 of the present invention;
FIG. 9 shows the oxygen reduction electrocatalytic performance of the catalyst prepared in example 3 of the present invention;
FIG. 10 shows the oxygen reduction electrocatalytic performance of the catalyst prepared in example 5 of the present invention;
FIG. 11 shows the oxygen reduction electrocatalytic performance of catalysts prepared in examples 1, 2, 3 of the present invention;
FIG. 12 is a graph showing the BET test results of the Co-MOF-derived cobalt/nitrogen/carbon composite material (Co-N-C (ZIF-67+ PEI)) prepared in example 1 and the Co-MOF-derived cobalt/nitrogen/carbon composite material (Co-N-C (ZIF-67)) prepared in comparative example 1;
FIG. 13 is an XPS spectrum of the Co-MOF-derived cobalt/nitrogen/carbon composite material (Co-N-C (ZIF-67+ PEI)) prepared in example 1 and the Co-MOF-derived cobalt/nitrogen/carbon composite material (Co-N-C (ZIF-67)) prepared in comparative example 1.
Detailed Description
In order to further illustrate the Co-MOF derived cobalt/nitrogen/carbon composite material and the preparation method thereof according to the present invention and achieve the intended purpose of the invention, the following detailed description is provided with reference to the preferred embodiments of a Co-MOF derived cobalt/nitrogen/carbon composite material and the preparation method thereof according to the present invention, and the detailed implementation, structure, characteristics and efficacy thereof are described below. In the following description, different "one embodiment" or "an embodiment" refers to not necessarily the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
The Co-MOF derived cobalt/nitrogen/carbon composite material and the method for preparing the same according to the present invention will be described in further detail with reference to the following specific examples:
the technical scheme of the invention is as follows:
(1) preparing a precursor solution: dissolving cobalt nitrate hexahydrate in methanol; and B, dissolving polyethyleneimine and dimethylimidazole in a methanol solution.
(2) Preparation of Co-MOF derived cobalt/nitrogen/carbon composite: 50ml of the prepared precursor solution A, B was respectively sucked up by two 50ml glass syringes and placed on a micro syringe pump. And setting a certain injection speed of the injection pump, and quickly pushing the two solutions into a reaction mold for quick mixing to obtain the suspension. Then, after the obtained suspension is centrifugally washed, the suspension is dried in a vacuum drying oven for 24 hours to prepare the Co-MOF composite material, and finally the product is placed in a tubular furnace to be treated for 2 hours by raising the temperature to 800-. After natural cooling to room temperature, the resulting sample was treated with dilute sulfuric acid, washed with deionized water until pH 7, and then dried in a vacuum oven at 80 ℃ for 24h to produce a Co-MOF derived cobalt/nitrogen/carbon composite.
The invention adopts high molecular polymer polyethyleneimine as a barrier material, so that the aggregation of metal organic framework nanoparticles in a high-temperature treatment process can be effectively avoided, and the derived cobalt/nitrogen/carbon catalyst has a better porous structure. More importantly, these characteristics allow the molecules associated with the reaction to diffuse readily to the active site, increasing the catalytic activity of oxygen reduction.
Oxygen reduction electrocatalytic performance test:
modification of the electrode: ultrasonically dispersing the prepared Co-MOF derived cobalt/nitrogen/carbon composite material into ultrapure water, then dripping the dispersion liquid onto an electrode, and drying at room temperature to obtain the electrode modified by the composite material.
The Co-MOF derived cobalt/nitrogen/carbon composites were tested for oxygen reduction electrocatalytic performance: the oxygen reduction electrocatalytic activity of the Co-MOF derived cobalt/nitrogen/carbon composite material is tested through an electrochemical workstation and a rotating disk electrode, a three-electrode system is adopted in the experiment, an electrode modified by the Co-MOF derived cobalt/nitrogen/carbon composite material is used as a working electrode, a platinum wire is used as a counter electrode, Ag/AgCL is used as a reference electrode, an electrolyte adopted in the electrochemical test is a KOH solution, the solution is saturated with oxygen for more than 30-40 min before the electrochemical test, the material is subjected to a linear scanning voltammetry test, and the strength of the electrocatalytic reduction activity of the material on oxygen is judged by observing the initial potential and the limiting current density of oxygen reduction.
Preferably, in the step (1), the mass ratio of the cobalt nitrate hexahydrate, the polyethyleneimine and the dimethylimidazole in the precursor liquid A, B is 0.736:0.306: 1.624. The cobalt nitrate hexahydrate and the polyethyleneimine have the best modification effect under the mass ratio. Cobalt nitrate hexahydrate and dimethyl imidazole in the mass ratio can form a Co-MOF composite material.
Preferably, in the step (2), the injection speed is 30-100 ml/min. At this injection rate, graphene-like structures can be formed.
Further preferably, in the step (2), the injection speed is 90 ml/min. At this injection rate, it is more favorable for the formation of graphene-like structures.
Preferably, in the step (2), the rotation speed of the centrifugal washing of the suspension is 7000-8000r/min, and further preferably, the centrifugal washing adopts a methanol solution.
Preferably, in the step (2), the Co-MOF composite material is treated at the temperature of 800-900 ℃ for 2 h.
Further preferably, in the step (2), the Co-MOF composite material is treated at 900 ℃.
Preferably, after said washing to neutrality, drying is carried out at 80 ℃ for 24 h.
Preferably, the concentration of the dilute sulfuric acid is 0.5 mol/L.
Preferably, the concentration of the dispersion in the oxygen reduction electrocatalytic performance test is 1-5 mg/ml.
Preferably, the electrolyte used in the electrochemical test in the oxygen reduction electrocatalytic performance test is 0.1 mol/LKOH.
Example 1.
The specific operation steps are as follows:
(1) preparing a precursor solution:
dissolving 0.736g of cobalt nitrate hexahydrate in (50ml) methanol to obtain a precursor solution A;
dissolving 0.306g of polyethyleneimine and 1.624g of dimethylimidazole in (50ml) methanol solution to obtain precursor solution B;
(2) preparation of Co-MOF derived cobalt/nitrogen/carbon composite:
50ml of the prepared precursor solution A, B was respectively sucked up by two 50ml glass syringes and placed on a micro syringe pump. The injection speed set by the injection pump is set to be 50ml/min, and the two solutions are quickly pushed into a reaction mold to be quickly mixed to obtain a suspension. Then, after the obtained suspension is centrifugally washed, the suspension is dried in a vacuum drying oven for 24 hours to prepare the Co-MOF composite material, and finally the product is placed in a tubular furnace to be treated for 2 hours by raising the temperature to 900 ℃ (argon atmosphere). Naturally cooling the obtained sample after the room temperature is reached, treating the obtained sample by using 0.5mol/L dilute sulfuric acid, washing the sample by using deionized water until the pH value is 7, and then drying the sample for 24 hours in a vacuum drying oven at the temperature of 80 ℃ to prepare the Co-MOF derived cobalt/nitrogen/carbon composite material;
(3) and (3) carrying out ultrasonic dispersion on the prepared cobalt/nitrogen/carbon composite material, then dripping 10 mu L of dispersion liquid with the concentration of 2mg/ml onto an electrode, and drying at room temperature to obtain the electrode modified by the composite material.
(4) The oxygen reduction electrocatalytic activity of the Co-MOF derived cobalt/nitrogen/carbon composite material (Co-N-C (ZIF-67+ PEI)) is tested through an electrochemical workstation and a rotating disk electrode, the experiment adopts a three-electrode system, the Co-MOF derived cobalt/nitrogen/carbon composite material modified electrode is a working electrode, a platinum wire is a counter electrode, Ag/AgCL is a reference electrode, an electrolysis liquid KOH solution adopted by the electrochemical test is saturated with oxygen for more than 30-40 min before the electrochemical test is carried out, the material is subjected to a linear scanning voltammetry test, the voltage range of the linear scanning voltammetry is selected from 0.2V to 1.0V, the scanning rate is 10mV/s (as shown in figures 3, 6 and 9), and the rotating speed is 625-rmp.
Implementation 2:
the procedure was the same as in example 1. The difference is as follows: the microinjection pump with the A/B solution was set to an injection rate of 70 ml/min.
Example 3:
the procedure was the same as in example 1. The difference is as follows: the microinjection pump with the A/B solution was set to an injection rate of 90 ml/min.
Example 4:
the procedure was the same as in example 1. The difference is as follows: the microinjection pump with the A/B solution was set to an injection rate of 30 ml/min.
Example 5:
the procedure was the same as in example 1. The difference is as follows: the microinjection pump with the A/B solution was set to an injection rate of 100 ml/min.
Example 6:
the procedure was the same as in example 1. The difference is as follows: the carbonization temperature in the tubular furnace in the step (2) is 800 ℃.
Example 7:
the procedure was the same as in example 1. The difference is as follows: the microinjection pump with the A/B solution was set to an injection rate of 70 ml/min. The carbonization temperature in the tubular furnace in the step (2) is 800 ℃.
Example 8:
the procedure was the same as in example 1. The difference is as follows: the microinjection pump with the A/B solution was set to an injection rate of 90 ml/min. The carbonization temperature in the tubular furnace in the step (2) is 800 ℃.
FIGS. 2, 5 and 8X-ray diffraction spectra of oxygen-reducing catalysts prepared in inventive examples 1, 2 and 3. As can be seen from the figure, the composite material containing N, C can be prepared by the technical scheme of the invention.
FIGS. 1, 4 and 7 are scanning electron micrographs of the oxygen-reducing catalysts prepared in examples 1, 2 and 3, respectively, of the present invention. As can be seen from the figure, the Co-MOF derived cobalt/nitrogen/carbon composite material prepared by the invention has a graphene structure, and the larger the injection speed is, the higher the graphene-like degree is.
FIGS. 3, 6, 9, 10, 11 show the electrocatalytic performance of oxygen reduction of the catalysts prepared in examples 1, 2, 3, 5 of the present invention. As can be seen from the figure, the electrocatalytic performance of the graphene-like degree of the Co-MOF derived cobalt/nitrogen/carbon composite material prepared by the invention is firstly increased and then reduced along with the increase of the injection speed.
Comparative example 1.
The procedure was the same as in example 1. The difference is as follows: no polyethyleneimine was used, only dimethylimidazole was used to provide the nitrogen source, and the mass of nitrogen in dimethylimidazole was very close to the mass of nitrogen in polyethyleneimine and dimethylimidazole in precursor liquid B in example 1.
BET tests were performed on the Co-MOF derived cobalt/nitrogen/carbon composite material (Co-N-C (ZIF-67+ PEI)) prepared in example 1 and the Co-MOF derived cobalt/nitrogen/carbon composite material (Co-N-C (ZIF-67)) prepared in comparative example 1. The results are shown in Table 1 and FIG. 12.
TABLE 1
The specific surface area (403.68 m) of Co-N-C (ZIF-67+ PEI) after the addition of Polyethyleneimine (PEI) was found by comparing the BET test results2·g-1) The specific surface area (139.47 m) is obviously higher than that of Co-N-C (ZIF-67)2·g-1)。
As can be seen from fig. 12, after Polyethyleneimine (PEI) is added, the mesoporous structure is significantly increased and improved. The addition of polyethyleneimine avoids excessive collapse of Co-MOF, and improves the specific surface area of the Co-MOF.
XPS tests were performed on the Co-MOF derived cobalt/nitrogen/carbon composite (Co-N-C (ZIF-67+ PEI)) prepared in example 1 and the Co-MOF derived cobalt/nitrogen/carbon composite (Co-N-C (ZIF-67)) prepared in comparative example 1. The results are shown in FIG. 13 and Table 2.
TABLE 2
The comparison of XPS spectra shows that the nitrogen content of the graphite containing pyridine nitrogen of Co-N-C (ZIF-67+ PEI) is higher than that of Co-N-C (ZIF-67) after Polyethyleneimine (PEI) is added, and the table shows that the nitrogen content of the Co-N-C (ZIF-67+ PEI) is higher than that of the Co-N-C (ZIF-67).
N can be converted into nitrogen with different structures such as graphite nitrogen, pyrrole nitrogen and the like in the carbonization process, the process is difficult to control, and the problem of collapse of a metal organic framework caused by the rise of pyrolysis temperature exists in the carbonization process. As can be seen from fig. 13, the nitrogen content increased and the graphite nitrogen and pyrrole nitrogen also increased after the addition of Polyethyleneimine (PEI) according to the present invention. It is shown that the nitrogen content can be increased and the graphite nitrogen can be increased after the addition of the polyethyleneimine.
The invention adopts a simple and feasible way to prepare the Co-MOF derived cobalt/nitrogen/carbon composite material. In the whole preparation process, polyethyleneimine plays an important role, so that excessive collapse of Co-MOF is avoided, the specific surface area of the Co-MOF is increased, and the content of nitrogen is increased. The high specific surface area and the synergistic effect of the cobalt-nitrogen structure enable the Co-MOF derived cobalt/nitrogen/carbon composite material to show excellent oxygen reduction electrocatalytic performance. The instantaneous nanometer sedimentation technology (FNP) has the advantages of simple method, low cost and short time, and can enlarge the production scale of materials. In general, a novel oxygen reduction electrocatalytic material is prepared by a simple and feasible method, and a new idea is provided for preparing a composite material electrocatalyst.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and any simple modification, equivalent change and modification made to the above embodiments according to the technical spirit of the present invention are within the scope of the technical solution of the present invention.
Claims (10)
1. A method for preparing a Co-MOF derived cobalt/nitrogen/carbon composite, comprising the steps of:
(1) preparing a precursor solution:
dissolving cobalt nitrate hexahydrate in methanol to obtain a precursor solution A;
dissolving polyethyleneimine and dimethyl imidazole in a methanol solution to obtain a precursor solution B;
(2) preparation of Co-MOF derived cobalt/nitrogen/carbon composite:
sucking the precursor liquid A, B with an injector respectively in equal amount, and placing on a micro-injection pump; under a certain injection speed, quickly pushing the two solutions into a reaction mold for quick mixing to obtain a suspension;
after the suspension is centrifugally washed, vacuum drying is carried out to obtain a Co-MOF composite material;
and (2) treating the Co-MOF composite material at the temperature of 900 ℃ under the conditions of oxygen isolation and 800-.
2. The production method according to claim 1,
in the step (1), the mass ratio of the cobalt nitrate hexahydrate, the polyethyleneimine and the dimethyl imidazole in the precursor liquid A, B is 0.736:0.306: 1.624.
3. The production method according to claim 1,
in the step (2), the injection speed is 30-100 ml/min.
4. The production method according to claim 3,
in the step (2), the injection speed is 90 ml/min.
5. The production method according to claim 1,
in the step (2), the centrifugal washing speed of the suspension is 7000-8000 r/min;
the centrifugal washing adopts methanol solution.
6. The production method according to claim 1,
in the step (2), the Co-MOF composite material is treated for 2 hours at 900 ℃.
7. The production method according to claim 6,
in the step (2), the Co-MOF composite material is treated at 900 ℃.
8. The production method according to claim 1,
after said washing to neutrality, drying at 80 ℃ for 24 h.
9. The production method according to claim 1,
the concentration of the dilute sulfuric acid is 0.5 mol/L.
10. A Co-MOF derived cobalt/nitrogen/carbon composite material, characterized in that it is prepared by the method of any one of claims 1 to 9.
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