CN113697791A - Defect-rich carbon material and preparation method and application thereof - Google Patents
Defect-rich carbon material and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a defect-rich carbon material and a preparation method and application thereof, wherein the preparation method of the defect-rich carbon material comprises the following steps: (1) preparing or taking a carbon precursor material; (2) heating a carbon precursor material and an oxidation etching agent to 600-1000 ℃ in a protective atmosphere, and reacting for 2-4 h to obtain an intermediate product; wherein, the oxidizing etching agent is a substance which can generate an etching effect on carbon or a substance which can generate an oxidizing substance by pyrolysis or release an oxidizing atmosphere; (3) and (4) carrying out post-treatment on the intermediate product to obtain the defect-rich carbon material. The defect-rich carbon material can be used as a catalyst for fuel cells, can replace the traditional catalyst, greatly improves the catalytic activity, has simple preparation process and simple and convenient operation, and can meet the requirements of different process flows.
Description
Technical Field
The invention relates to the field of carbon-containing catalytic materials, in particular to a defect-rich carbon material and a preparation method and application thereof.
Background
The fuel cell is a novel power generation device which directly converts chemical energy generated by oxidation reduction of fuel and oxidant into electric energy, and has the advantages of environmental protection, high energy conversion efficiency, quick start and close and the like. However, the development of fuel cells is still limited by problems such as a slow kinetics of the cathode Oxygen Reduction Reaction (ORR) and a limited practical energy density. The oxygen reduction catalyst of the air cathode plays a crucial role in the performance of the battery, and largely determines the energy efficiency of the battery as a whole. Designing and developing efficient oxygen reduction catalysts has become a key technology and research hotspot for improving the electrochemical performance of fuel cells.
The oxygen reduction electrocatalyst is one of the key materials of the fuel cell, and the current commercial oxygen reduction catalyst mainly uses Pt/C, but the Pt resource is limited, the price is high, and the stability of the oxygen reduction electrocatalyst needs to be further improved. The defective carbon material has the advantages of low cost and excellent stability, and is a novel oxygen reduction catalyst material with great potential. However, the catalytic activity of the carbon-based catalyst is still far from that of commercial Pt/C, and the design of a synthesis strategy with industrialization and universality to improve the catalytic activity of the carbon material is a research and development hotspot of the current carbon-based catalyst.
At present, a carbon material is obtained by mainly calcining a carbon precursor at high temperature, and the carbon material with a certain catalytic action is obtained by adjusting and controlling the defects of a derived carbon material by changing the composition and the structure of the precursor. In addition, N doping is an effective way for improving the catalytic activity of the carbon material at present. However, the conventional synthesis of the N-doped carbon material is to mix and calcine a nitrogen source and a carbon source, so that the exposure of active nitrogen is difficult to realize, and the catalytic activity is not as expected. Meanwhile, in the traditional carbon material synthesis process, different carbon precursors (namely different types of nitrogen sources and carbon sources) are adopted, so that the carbon materials derived from the carbonized carbon materials are different in nitrogen defect form, but the catalytic performance of the carbon materials is difficult to greatly improve due to the lack of defect sites with high-efficiency catalytic activity. Therefore, compared with the carbon material obtained by deriving carbon precursors with different structure types, the method for developing a universal carbon-based defect promotion strategy to improve the oxygen reduction catalytic activity of the carbon-based material is a research focus of the current catalyst development.
Disclosure of Invention
The invention provides a defect-rich carbon material and a preparation method and application thereof, which are used for solving the technical problems of low catalytic activity and complicated design and synthesis steps of the existing carbon material.
In order to solve the technical problems, the invention adopts the following technical scheme:
a method for preparing a defect-rich carbon material, comprising the steps of:
(1) preparing or taking a carbon precursor material which can form reducing carbon under high-temperature pyrolysis;
(2) carrying out high-temperature pyrolysis on the carbon precursor material and an oxidation etching agent in a protective atmosphere to form carbon vacancies and/or abundant defective carbon, and cooling to obtain an intermediate product; wherein, the oxidizing etching agent can generate etching action on carbon or generate oxidizing substances or release oxidizing atmosphere substances in the pyrolysis process;
(3) and carrying out post-treatment on the intermediate product to obtain the defect-rich carbon material.
The design idea of the technical scheme is that the oxidizing etchant and the carbon precursor material are heated together, the oxidizing etchant etches the precursor in the process, or the oxidizing etchant is pyrolyzed to generate oxidizing substances or oxidizing gas to etch the precursor locally, and the main action principle of the oxidizing etchant is as follows: the precursor gradually begins to be carbonized and reformed to form graphitized carbon material in the pyrolysis process, while the graphitic carbon has stronger reducibility, and because the oxidizing etching agent has strong oxidizing property, or oxidizing substances or oxidizing gases generated by the oxidizing etching agent in the pyrolysis process and carbon with reducibility have partial redox reaction (C + O)oxy→ CO + Ored, oxy and Ored are oxidizing species, reduced species, respectively), local carbon is etched out in the form of CO, leaving a large number of carbon vacancies and forming abundant defect carbon. Compared with the prior art that the structure of the carbon precursor needs to be designed and synthesized in advance for forming the carbon defect sites, the method is suitable for most carbon precursor materials, can greatly avoid the difficulty of structural design and synthesis of the precursor, and has practicability and universality.
As a further preferable mode of the above technical solution, the oxidizing etchant includes a metal oxygen-containing compound, a metal halide, a nonmetal compound, and a halogen simple substance. Making
As a further preferable mode of the above technical solution, the oxidizing etchant includes at least one of a metal oxygen-containing compound, a metal halide and a simple substance of halogen; the metal oxygen-containing compound includes at least one of a metal oxide, a metal hydroxide, a metal peroxide, a strongly oxidizing salt, a carboxylate, and a nitrate. The three types of oxidation etching agents can generate oxidation etching effect on carbon or can generate etching effect on the carbon material per se in the pyrolysis process, and the oxidation etching agents are convenient to remove after pyrolysis, complex impurity removal processes are not required to be introduced, loss of active sites of the carbon material matrix is avoided, and meanwhile, the oxidation etching agents are low in cost, easy to obtain, suitable for mass production and beneficial to industrialization. The oxidizing and etching agent capable of directly etching the carbon precursor comprises metal oxides (sodium oxide, potassium oxide, magnesium oxide, calcium oxide, zinc oxide, iron oxide and the like) and metal hydroxides (potassium hydroxide, sodium hydroxide, iron hydroxide and the like). The oxidizing etchant for etching a carbon precursor by generating an oxidizing substance by pyrolysis includes metal peroxides (sodium peroxide, magnesium peroxide, barium peroxide, calcium peroxide, etc.), strongly oxidizing salts (potassium permanganate, potassium dichromate, potassium chlorate, etc.), carboxylates (zinc acetate, sodium acetate, etc.), nitrates (sodium nitrate, potassium nitrate, zinc nitrate, copper nitrate, cobalt nitrate, sodium nitrite, etc.), metal halides (including sodium chloride, potassium chloride, sodium bromide, sodium iodide, potassium bromide, zinc chloride, zinc bromide, iron chloride, etc.), non-metallic compounds (hydrogen peroxide, peracetic acid, ammonium chloride, ammonium nitrate, ammonium nitrite, etc.), elemental halogens (liquid bromine, elemental iodine, etc.).
As a further optimization of the technical scheme, the addition amount of the oxidation etching agent in the step (2) is 0.2-8 times of the mass of the precursor material. The adding proportion of the oxidation etching agent is different according to the carbon content of the precursor, and the oxidation etching agent can effectively carry out partial etching on a small amount of carbon to construct carbon intrinsic defect sites under the premise of a certain carbonization yield within the proportion range.
In a further preferred embodiment of the present invention, the carbon precursor material is a carbon precursor material in which carbon defect sites are not formed
As a further preferable mode of the above aspect, the carbon precursor material isThe nitrogen-containing material contains nitrogen elements. The carbon precursor material containing nitrogen element can introduce extrinsic defects into the carbon material by doping N element, so that the carbon material has intrinsic defects and extrinsic defects at the same time, and the carbon material is promoted to enhance O by virtue of nonuniform electron cloud density distribution and change of space curvature of the carbon layer caused by N doping and intrinsic carbon defects2The adsorption acting force of the carbon material is adjusted, the adsorption energy of the oxygen-containing intermediate in the oxygen reduction process is adjusted to promote the process of the oxygen reduction reaction, the oxygen reduction catalytic performance of the carbon material is greatly improved, meanwhile, N is doped into the carbon network structure in the pyrolysis process of the N-containing precursor, the N-doped and defect carbon cooperative sites are formed, and the defect site density of the carbon material is further improved by combining the carbon defect left by the oxidation etching.
As a further preferred aspect of the above technical solution, the carbon precursor material includes at least one of a metal-organic framework complex and a carbon-containing polymer. Compared with other common carbon precursor materials (such as common carbon sources of glucose, melamine, citric acid, ribose and the like), the two carbon precursor materials have a certain thermal stability structure, are easy to carbonize to form a carbon material, have no impurities or only have a small amount of impurities which are easy to remove after carbonization, can obtain the carbon material with a richer pore structure and a larger specific surface area after calcination, and are beneficial to the promotion of catalytic activity.
As a further preferred aspect of the above technical solution, the metal organic framework complex is one or a combination of several of a ZIF series complex, a CPL series complex, an MIL series complex, a hexamethylenetetramine complex, and a metal phthalocyanine complex, and such a precursor has a high carbonization yield, and can avoid excessive oxidation etching to bring a large amount of carbon loss, thereby obtaining a carbon material with a high yield.
As a further optimization of the technical scheme, the carbon-containing polymer is one or a combination of more of polypyrrole, polyaniline, polyacrylamide and polyacrylic acid, and the precursor is simple to prepare, high in carbonization yield and easy to obtain a carbon material.
As a further preferred aspect of the above technical solution, the post-treatment in step (3) includes soaking, washing and filtering operations.
Based on the same technical concept, the invention also provides a defect-rich carbon material which is prepared by the preparation method of the technical scheme.
The design idea of the technical scheme is that the carbon material prepared by the method can be used for replacing the traditional commercial noble metal Pt-based catalyst, the catalytic activity is greatly improved (the maximum half-wave potential lifting amplitude can reach more than 200 mV), the catalytic performance and the cycle stability of the carbon material are superior to those of a Pt/C catalytic material, the production cost is low, and the carbon material has a wide market prospect.
Based on the same technical concept, the invention also provides an application of the defect-rich carbon material or the defect-rich carbon material prepared by the preparation method, and the defect-rich carbon material is applied to a fuel cell as an electrocatalyst.
Compared with the prior art, the invention has the advantages that:
(1) according to the preparation method, the carbon precursor is etched through the oxidizing atmosphere/oxide generated in the pyrolysis process of the oxidant, so that the defect sites of the carbon material, particularly carbon intrinsic defects such as carbon vacancies, carbon edges and the like, are promoted; meanwhile, the catalytic activity of the carbon-based catalyst is greatly improved by utilizing N-doped defects generated in the pyrolysis process of the N-containing carbon precursor in cooperation with intrinsic defect sites and N-doped defect sites; the preparation process is simple, the operation is simple and convenient, the structure of the carbon precursor and the type of the oxidant can be adjusted according to the requirements, the method is suitable for most carbon precursor materials, the difficulty in structural design and synthesis of the precursor can be greatly avoided, the practicability and universality are realized, the operation flexibility is strong, and the method can be suitable for the requirements of different process flows;
(2) the defect carbon material prepared by the preparation method can be used for replacing the traditional commercial noble metal Pt-based catalyst, the catalytic activity of the defect carbon material is greatly improved (the maximum half-wave potential lifting amplitude can reach more than 200 mV), and the defect carbon material has better catalytic performance and cycle stability than Pt/C catalytic materials.
Drawings
FIG. 1 is a scanning electron micrograph of a defect-rich carbon material of example 1;
FIG. 2 is a comparison of linear cyclic voltammograms of the defect-rich carbon material of example 1.
FIG. 3 is a scanning electron micrograph of the defect-rich carbon material of example 2;
FIG. 4 is a comparison of linear cyclic voltammograms of the defect-rich carbon material of example 2;
FIG. 5 is a scanning electron micrograph of the defect-rich carbon material of example 3;
FIG. 6 is a comparison of linear cyclic voltammograms of the defect-rich carbon material of example 3; (ii) a
FIG. 7 is a scanning electron micrograph of the defect-rich carbon material of example 3;
FIG. 8 is a comparison of linear cyclic voltammograms of the defect-rich carbon material of example 4;
FIG. 9 is a scanning electron micrograph of the defect-rich carbon material of example 5;
FIG. 10 is a comparison of linear cyclic voltammograms of the defect-rich carbon material of example 5;
FIG. 11 is a linear cyclic voltammogram of a commercial Pt/C catalyst.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
Example 1:
in the preparation method of the defect-rich carbon material, in the embodiment, a metal organic framework complex of zinc-benzimidazole (Zn-BZIM) is used as a carbon precursor material, and an oxidation etching strategy is used to promote defect sites of the Zn-BZIM derived carbon material so as to promote the electrocatalysis performance of the Zn-BZIM derived carbon material, and the specific preparation method is as follows:
(1) preparing a carbon precursor material: dissolving 10mmol of zinc nitrate in 100mL of methanol solution, dissolving 20mmol of benzimidazole in 100mL of methanol solution, mixing the two solutions after complete dissolution, stirring for 12h at room temperature, and standing for 2h at normal temperature to obtain white complex precipitate. Carrying out vacuum filtration on the suspension, washing the suspension with an alcoholic solution for three times, and drying the suspension at 60 ℃ for 12 hours to obtain a white metal organic framework complex of zinc-benzimidazole (Zn-BZIM);
(2) placing 300mg of Zn-BZIM as carbon precursor material in a porcelain boat, placing 600mg of sodium chloride (NaCl) as oxidation etching agent in the porcelain boat, placing in a sealed tube furnace, and performing Ar/H oxidation treatment in the presence of Ar/H2Heating to 900 ℃ from room temperature at the speed of 5 ℃/min under the atmosphere, keeping the temperature for 2 hours, and naturally cooling to obtain an intermediate product;
(3) and soaking the obtained intermediate product in water overnight, washing and filtering to obtain the product, namely the defect-rich carbon material ON/C-1.
Putting 300mg of Zn-BZIM obtained in the step (1) as a carbon precursor into a porcelain boat, and performing Ar/H2And heating the mixture to 900 ℃ from room temperature at the speed of 5 ℃/min in the atmosphere, keeping the temperature for 2 hours, naturally cooling and cooling to obtain an N-doped carbon material N/C-1, wherein the N-doped carbon material obtained without oxidation etching is used for comparing with the defect-rich carbon material ON/C-1 in the embodiment.
Subjecting the obtained defect-rich carbon material ON/C-1 to field emission scanning electron microscope (SEM, JSM-7610F, JEOL)TM) The grain size and the micro morphology of the metal organic framework are observed, a scanning electron microscope image of the metal organic framework is shown in figure 1, and the figure shows that the metal organic framework is oxidized and etched by halide ON the basis of the Zn-BZIM, and the ON/C-1 is changed into a printed cake-shaped structure after the metal organic framework is oxidized, etched and calcined.
The electrochemical performance test of the obtained defect-rich carbon material ON/C-1, the carbon material N/C-1 obtained without the peroxide etching and commercial 20 wt% Pt/C is carried out, and the test method is as follows: 6mg of the catalyst material is put into a 2mL small centrifugal tube, 0.98mL of absolute ethyl alcohol is accurately transferred into the small centrifugal tube by a 1mL pipette, and finally 20 mu L of 5% Nafion emulsion is absorbed into the centrifugal tube by a liquid transfer gun. And (4) carrying out ultrasonic treatment for one hour until the solution is uniformly dispersed without obvious particle precipitation. The circular ring electrode of the rotating disc is a glassy carbon electrode with the diameter of 5mm, and the glassy carbon electrode needs to be subjected to Al treatment in advance2O3Polishing with polishing powder, washing with distilled water, and drying with a piece of lens wiping paper. And (3) absorbing 8 mu L of uniformly dispersed catalyst sample by using a pipette during testing, uniformly and flatly paving the catalyst sample in the center of the polished glassy carbon electrode, and naturally airing to obtain the working electrode.An NOVA2.0 electrochemical workstation is used for carrying out electrochemical performance test, a three-electrode system is adopted for testing, a reference electrode is an Ag/AgCl electrode, a counter electrode is a carbon rod, and a working electrode is a glassy carbon electrode loaded with a catalyst. After the three-electrode system is assembled, in order to ensure the saturated oxygen condition, oxygen needs to be introduced into 0.1MKOH electrolyte for half an hour in advance, and then linear cyclic voltammetry scanning is carried out, wherein the scanning interval is 0.20 to-0.90 Vvs.Ag/AgCl, and the scanning speed is 10mV s-1。
The test results of the defect-rich carbon material ON/C-1 and the carbon material N/C-1 obtained without the peroxide etching are shown in FIG. 2, and the test results of the commercial 20 wt% Pt/C material are shown in FIG. 11, and it can be seen that the defect-rich carbon material has excellent oxygen reduction catalytic activity, which is superior to the carbon material N/C-1 obtained without the peroxide etching and the commercial 20 wt% Pt/C performance, and the carbon material with high activity can be obtained by the method, and the action mechanism is mainly that the halide can generate hydrogen chloride acid gas during the calcination process, partially etches the precursor, causes the formation of carbon defects, and exposes rich defect sites. The main catalytic performance of the catalyst formed by oxidation, etching and carbonization mainly comes from the synergistic action sites of carbon intrinsic defects and N-doped extrinsic defects.
Example 2:
in the preparation method of the defect-rich carbon material, in the embodiment, a zinc-2-methylimidazole (ZIF-8) metal organic framework complex is used as a carbon precursor material, and an oxidation etching strategy is used for improving defect sites of a ZIF-8 derived carbon material to improve the electrocatalysis performance of the carbon precursor material, and the preparation method specifically comprises the following steps:
(1) preparing a carbon precursor material: dissolving 20mmol of zinc nitrate in 100mL of methanol solution, dissolving 80mmol of 2-methylimidazole in 100mL of methanol solution, mixing the two solutions after complete dissolution, stirring for 12h at room temperature, and standing for 24h at normal temperature to obtain white complex precipitate. Centrifuging the solution three times at 8000r/min, washing with methanol solution three times, and drying at 60 deg.C for 12 hr to obtain white metal-organic framework complex of zinc-2-methylimidazole (ZIF-8);
(2) taking 400mg of the obtained ZIF-8 as a carbon precursor material, placing the carbon precursor material in a porcelain boat, and taking 200mg of sodium nitrite (NaNO)2) Heating the ceramic boat serving as an oxidation etching agent to 900 ℃ from room temperature at the speed of 5 ℃/min in a high-temperature tube furnace protected by Ar, keeping the temperature for 2 hours, and naturally cooling to obtain an intermediate product;
(3) and soaking the obtained intermediate product in an aqueous solution overnight to remove residual metal oxide impurities, and filtering, washing and drying to obtain the defect-rich carbon material ON/C-2.
And (2) placing 400mg of ZIF-8 obtained in the step (1) as a carbon precursor in a porcelain boat, heating the carbon precursor to 900 ℃ from room temperature at a speed of 5 ℃/min under Ar atmosphere, keeping the temperature for 2h, naturally cooling and cooling to obtain an N-doped carbon material N/C-2, wherein the N-doped carbon material obtained without oxidation etching is used for comparing with the defect-rich carbon material ON/C-2 in the embodiment.
Subjecting the obtained defect-rich carbon material ON/C-2 to field emission scanning electron microscope (SEM, JSM-7610F, JEOL)TM) The grain size and the micro morphology of the carbon material are observed through detection, a scanning electron microscope image of the carbon material is shown in figure 3, and the scanning electron microscope image shows that the carbon material carbonized by ZIF-8 presents an obvious fold lamellar structure under the action of the oxidation etching of nitrite.
The obtained defect-rich carbon material ON/C-2 and the carbon material N/C-2 obtained without the peroxide etching were subjected to electrochemical performance tests in accordance with the test method in example 1.
The test results for the defect-rich carbon material ON/C-2 and carbon material N/C-2 obtained without the peroxide etching are shown in FIG. 4, from which it can be seen that, the defect-rich carbon material has excellent oxygen reduction catalytic activity, compared with carbon material N/C which is not subjected to peroxide etching, ON/C-2 shows more positive half-wave potential and larger limiting current and is superior to commercial 20 wt% Pt/C, and the catalytic activity of the whole material can be improved by the method, the action mechanism of the method mainly lies in the strong oxidizing property of nitrite, a local carbon precursor is oxidized to form abundant carbon defect sites in the mixing and calcining process of the nitrite and the carbon precursor, and the calcined material has abundant carbon defect structures and exposes abundant active sites, so that the defect sites of the carbon material are improved, and the catalytic performance is greatly improved.
Example 3:
in the preparation method of the defect-rich carbon material of the embodiment, polypyrrole is used as a carbon precursor material, and the specific preparation method is as follows:
(1) preparing a carbon precursor material: 40mmol of pyrrole monomer was dissolved in 300mL of an alcohol/water mixture (ethanol: water: 1), and 40mmol of persulfuric acid was dissolved in 25mL of water. Slowly and dropwise adding the ammonium persulfate solution into the pyrrole solution, and stirring for 12 hours in an ice bath environment to obtain a dark green suspension solution. And filtering, washing and drying the obtained suspension to obtain dark green powder, namely the polypyrrole Ppy.
(2) Placing 300mg of the Ppy in a big porcelain boat, and taking 150mg of sodium nitrate (NaNO)3) And (2) placing the small porcelain boat filled with sodium nitrate into the large porcelain boat filled with Ppy, placing the small porcelain boat in a high-temperature tube furnace protected by Ar, heating the small porcelain boat to 900 ℃ from room temperature at a speed of 10 ℃/min, keeping the temperature for 3 hours, and naturally cooling to obtain black powder which is the defect-rich carbon material ON/C-3 without subsequent treatment.
And (2) placing 300mg of Ppy obtained in the step (1) as a carbon precursor in a porcelain boat, heating the Ppy to 900 ℃ from room temperature at a speed of 10 ℃/min under Ar atmosphere, keeping the temperature for 2h, naturally cooling and cooling to obtain an N-doped carbon material N/C-3, wherein the N-doped carbon material obtained without oxidation etching is used for comparing with the defect-rich carbon material ON/C-3 of the embodiment.
Subjecting the obtained defect-rich carbon material ON/C-3 to field emission scanning electron microscope (SEM, JSM-7610F, JEOL)TM) And (3) detecting, observing the grain size and the microstructure, wherein a scanning electron microscope image of the material is shown in figure 5, and oxidizing, etching and calcining the material in a polypyrrole precursor to obtain a polypyrrole carbonized material with small particles, wherein the morphology structure of the polypyrrole carbonized material is consistent with that of polypyrrole obtained by direct carbonization.
And carrying out electrochemical performance test ON the obtained defect-rich carbon material ON/C-3 and the carbon material N/C-3 obtained without peroxide etching, wherein the test method is consistent with that in the embodiment 1.
The results of testing the defect-rich carbon material ON/C-3 and the carbon material N/C-3 obtained without the hydrogen peroxide etching are shown in FIG. 6, from which it can be seen that the catalyst shows a half-wave potential rise of nearly 200mV and a larger limiting current compared to the material without the hydrogen peroxide etching, and is comparable to the commercial 20 wt% Pt/C performance. The action mechanism is mainly that a large amount of NO and O are generated in the calcining process through sodium nitrate2And the carbon material with rich carbon defects is obtained by oxidizing, etching and carbonizing the polypyrrole precursor in the calcining process by using the etching gas with the oxidizing property. The carbon intrinsic defect is introduced by the method, and the carbon intrinsic defect is cooperated with the N-doped defect sites, so that the catalytic activity of the carbon material can be greatly improved.
Example 4:
in the preparation method of the defect-rich carbon material, in the embodiment, a zinc-2-methylimidazole (ZIF-8) metal organic framework complex is used as a carbon precursor material, and zinc acetate is used for oxidation etching, and the specific preparation method is as follows:
(1) preparing a carbon precursor material: dissolving 50mmol of zinc nitrate in 100mL of methanol solution, dissolving 200mmol of 2-methylimidazole in 100mL of methanol solution, mixing the two solutions after complete dissolution, stirring for 12h at room temperature, and standing for 24h at normal temperature to obtain white complex precipitate. Filtering the suspension, washing with methanol solution for three times, and drying at 60 deg.C for 12 hr to obtain white zinc-2-methylimidazole (ZIF-8) metal-organic framework complex;
(2) 500mg of the obtained ZIF-8 was used as a carbon precursor material with 500mg of zinc acetate (Zn (CH)3COO)2) Mixing with ethanol solution, stirring and drying ethanol at 60 deg.C to obtain mixture of ZIF-8 and zinc acetate, and adding the mixture into N2Heating the mixture to 900 ℃ from room temperature at the speed of 7 ℃/min in a protected high-temperature tube furnace, keeping the temperature for 2 hours, and naturally cooling to obtain an intermediate product;
(3) soaking the intermediate product in 0.5mol/L sulfuric acid solution overnight, filtering, washing and drying to obtain the product ON/C-4 material.
Putting 500mg of ZIF-8 obtained in the step (1) as a carbon precursor in a porcelain boat, and adding N2And heating the mixture to 900 ℃ from room temperature at the speed of 7 ℃/min in the atmosphere, keeping the temperature for 2 hours, naturally cooling and cooling to obtain an N-doped carbon material N/C-4, wherein the N-doped carbon material obtained without oxidation etching is used for comparing with the defect-rich carbon material ON/C-4 in the embodiment.
Subjecting the obtained defect-rich carbon material ON/C-4 to field emission scanning electron microscope (SEM, JSM-7610F, JEOL)TM) The grain size and the micro morphology of the carbon sheet are observed through detection, a scanning electron microscope image of the carbon sheet is shown in FIG. 7, and it can be seen from the image that the carbon sheet with a sheet structure and a rich pore structure is obtained after zinc acetate is mixed in ZIF-8 for oxidation, etching and calcination.
And carrying out electrochemical performance test ON the obtained defect-rich carbon material ON/C-4 and the carbon material N/C-4 obtained without peroxide etching, wherein the test method is consistent with that in the embodiment 1.
The test results for the defect-rich carbon material ON/C-4 and the carbon material N/C-4 obtained without the hydrogen peroxide etching are shown in FIG. 8, from which it can be seen that the defect-rich carbon material has excellent oxygen reduction catalytic activity, and from which it can be seen that the catalyst shows a more positive half-wave potential and a larger limiting current than the material N/C-4 without the hydrogen peroxide etching. The action mechanism of the method is mainly that the oxidation etching mechanism of zinc sulfate is that zinc acetate is converted into ZnO in the heating process and simultaneously a large amount of CO is released2CO while making pore on the material2The carbon material reacts with ZnO and a local carbon precursor to generate CO and Zn simple substances, so that local carbon defects are caused, the defect site density of the carbon material is improved, and the improvement of the catalytic activity of the carbon material can be realized through zinc acetate oxidation etching.
Example 5:
in the preparation method of the defect-rich carbon material, in the embodiment, a zinc/cobalt-2-methylimidazole (Zn/Co-BZIF) metal organic framework complex is used as a carbon precursor material, and sodium bromide is used for oxidation etching to obtain a Co-N Co-doped carbon material, and the specific preparation method is as follows:
(1) preparing a carbon precursor material: dissolving 47.5mmol of zinc nitrate and 2.5mmol of cobalt nitrate in 100mL of methanol, dissolving 200mmol of 2-methylimidazole in 100mL of methanol solution, mixing the two solutions after complete dissolution, stirring at room temperature for 6h, and standing at room temperature for 24h to obtain a blue-violet complex precipitate. Filtering the suspension, washing with methanol solution for three times, and drying at 60 deg.C for 12 hr to obtain blue-violet zinc/cobalt-2-methylimidazole (Zn/Co-BZIF) metal-organic framework complex;
(2) putting 200mg of Zn/Co-BZIF obtained as a carbon precursor material into a porcelain boat, and taking 100mg of iodine simple substance (I)2) As an oxidizing etchant in a porcelain boat at Ar/H2Heating the mixture to 800 ℃ from room temperature at the speed of 5 ℃/min in a protected high-temperature tube furnace, keeping the temperature for 2 hours, and naturally cooling to obtain an intermediate product;
(3) soaking the intermediate product in 0.5mol/L sulfuric acid solution overnight, filtering, washing and drying to obtain the defect-rich carbon material OCo, N/C.
Putting 200mg of Zn/Co-BZIF obtained in the step (1) as a carbon precursor into a porcelain boat, and putting the carbon precursor in Ar/H2Heating the mixture to 800 ℃ from room temperature at a speed of 5 ℃/min in the atmosphere, keeping the temperature constant for 2 hours, naturally cooling and cooling the mixture, soaking the mixture in a 0.5mol/L sulfuric acid solution for a while, filtering, washing and drying the mixture to obtain Co and N Co-doped carbon materials Co and N/C, wherein the Co and N doped carbon materials obtained without oxidation etching are used for comparing with the defect-rich carbon materials OCo and N/C in the embodiment.
Subjecting the obtained defect-rich carbon material OCo, N/C to field emission scanning electron microscope (SEM, JSM-7610F, JEOL)TM) And (3) detecting, and observing the grain size and the microstructure of the carbonized material, wherein a scanning electron microscope image of the carbonized material is shown in FIG. 9, and the carbonized material with a cubic structure is obtained by performing oxidation etching calcination in a Zn/Co-BZIF precursor.
The obtained defect-rich carbon material OCo, N/C and the carbon material Co, N/C obtained without the hydrogen peroxide etching were subjected to electrochemical performance tests, and the test methods were the same as those in example 1.
The results of testing the defect-rich carbon material OCo, N/C and the carbon material Co, N/C obtained without the hydrogen peroxide etching are shown in FIG. 10, from which it can be seen that the defect-rich carbon material shows a more positive half-wave potential rise and a larger limiting current than the material without the hydrogen peroxide etching, and is comparable to the commercial 20 wt% Pt/C performance. The action mechanism of the method is mainly characterized in that iodine simple substance is combined with hydrogen in argon/hydrogen mixed gas to form corrosive acid gas hydroiodic acid, a carbon precursor is etched, the structure of the carbon precursor is damaged to generate a large number of carbon defect sites in the carbonization process, the abundant carbon defect sites are constructed through an oxidation etching mechanism, so that the active sites of the material are greatly improved, the adsorption force of the material on oxygen is enhanced, and the catalytic activity of the carbon material can be greatly improved.
The embodiment shows that the carbon material prepared by the method can completely replace the current commercial noble metal Pt-based catalyst, the preparation method obviously improves the catalytic activity of carbon materials derived from different carbon precursors, the carbon intrinsic defect sites constructed by the method are cooperated with the extrinsic defect sites generated by N doping to greatly improve the catalytic activity of the material, and the method has universality, practicability and economy. Meanwhile, the selection of the oxidant and the carbon precursor is flexible, a proper oxidation etching strategy can be selected according to actual requirements and a process flow, the cost of the oxygen reduction catalyst is reduced, the process flow is simplified, the manufacturing cost of the air cathode is further reduced, and the method has a wide market prospect.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-described embodiments. Modifications and variations that may occur to those skilled in the art without departing from the spirit and scope of the invention are to be considered as within the scope of the invention.
Claims (10)
1. A method for preparing a defect-rich carbon material, comprising the steps of:
(1) preparing or taking a carbon precursor material which can form reducing carbon under high-temperature pyrolysis;
(2) carrying out high-temperature pyrolysis on the carbon precursor material and an oxidation etching agent in a protective atmosphere to form carbon vacancies and/or abundant defective carbon, and cooling to obtain an intermediate product; wherein, the oxidizing etching agent is a substance capable of generating an etching effect on carbon or a substance capable of generating an oxidizing substance or releasing an oxidizing atmosphere in a pyrolysis process;
(3) and carrying out post-treatment on the intermediate product to obtain the defect-rich carbon material.
2. The method for producing a defect-rich carbon material as claimed in claim 1, wherein the oxidizing etchant comprises at least one of a metal oxygen-containing compound, a metal halide and an elemental halogen.
3. The method for producing a defect-rich carbon material as claimed in claim 2, wherein the metal oxygen-containing compound comprises at least one of a metal oxide, a metal hydroxide, a metal peroxide, a strong oxidizing salt, a carboxylate and a nitrate.
4. The method for preparing a defect-rich carbon material as claimed in claim 1, wherein the amount of the oxidizing etchant added in step (2) is 0.2-8 times the mass of the precursor material.
5. The method for producing a defect-rich carbon material as claimed in claim 1, wherein the pyrolysis in the step (2) is carried out at a temperature of 600 to 1000 ℃ for 2 to 4 hours.
6. The method for producing a defect-rich carbon material according to any one of claims 1 to 5, wherein the carbon precursor material is a carbon precursor material in which carbon defect sites are not formed.
7. The method of producing a defect-rich carbon material as claimed in claim 6, wherein the carbon precursor material contains nitrogen element, and the carbon precursor material includes at least one of a metal-organic framework complex and a carbon-containing polymer.
8. The method for producing a defect-rich carbon material as claimed in claim 7, wherein the metal-organic framework complex is one or a combination of several of a ZIF series complex, a CPL series complex, an MIL series complex, a hexamethylenetetramine complex and a metal phthalocyanine complex; the carbon-containing polymer is one or a combination of more of polypyrrole, polyaniline, polyacrylamide and polyacrylic acid.
9. A defect-rich carbon material produced by the production method according to any one of claims 1 to 8.
10. Use of the defect-rich carbon material of claim 9 or the defect-rich carbon material produced by the production method of any one of claims 1 to 8 as an electrocatalyst for fuel cells.
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