CN111584889B

CN111584889B - Zinc-containing monatomic catalyst and preparation method and application thereof

Info

Publication number: CN111584889B
Application number: CN202010475821.6A
Authority: CN
Inventors: 范梁栋; 徐括峰
Original assignee: Shenzhen University
Current assignee: Shenzhen University
Priority date: 2020-05-29
Filing date: 2020-05-29
Publication date: 2021-05-11
Anticipated expiration: 2040-05-29
Also published as: CN111584889A

Abstract

The invention discloses a zinc-containing monatomic catalyst, and a preparation method and application thereof. According to the invention, 2-methylimidazole zinc salt (ZIF8) is used as a zinc precursor, a zinc intermediate is obtained by low-temperature calcination, then the low-zinc intermediate is etched (and loaded), and finally the high-temperature calcination is carried out to prepare the zinc-containing monatomic catalyst. The method has the following advantages: the process is simple and controllable, the zinc content does not need to be strictly controlled, and a carrier material does not need to be adopted; the low-temperature calcination and etching before the high-temperature calcination can effectively prevent the zinc atoms from agglomerating; the obtained pure zinc monatomic catalyst has good catalytic activity, high stability and better anti-poisoning capability; the obtained loaded zinc-containing monatomic catalyst can further improve the catalytic activity of the pure zinc monatomic catalyst or meet the requirements of different catalytic systems.

Description

Zinc-containing monatomic catalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of electrocatalysis, in particular to a zinc-containing monatomic catalyst and a preparation method and application thereof.

Background

High energy density, high efficiency zinc-air cell, fuel cell are promising energy storage devices in the future, and as long as there is a suitable cathode oxygen reduction catalyst, zinc-air cell, fuel cell will occupy an important position in the future energy storage and conversion field. As a special supported non-noble metal catalyst, the monatomic catalyst specially means that all metal components on the carrier exist in a monatomic dispersion mode, the catalytic active sites of the monatomic catalyst are exposed to the maximum extent, when the dispersion degree of particles reaches the monatomic size, more and more new characteristics relative to a nanoscale material can be caused, such as rapidly increased surface free energy, quantum size effect, unsaturated coordination environment, strong interaction of metal and the carrier and the like, the monatomic catalyst is endowed with excellent activity, selectivity and utilization efficiency, the catalytic performance can be further improved, and the manufacturing cost is reduced from the aspect of atom economy. And the relative stability of the monatomic dispersion catalyst can be effectively maintained through the interaction of the monatomic dispersion catalyst and the carrier. Due to their high activity and selectivity, monatomic catalysts have shown great potential for use in industrial catalysis and related fields.

So far, there have been many reports of metal (M) -nitrogen (N) -carbon (C) -based monatomic catalysts such as Fe, Co, Ni, and Mn having redox couples and noble metals, in which doping of the metal can adjust the electronic structure of the adjacent carbon atom method, thereby accelerating chemisorption and activation of the reactant and having high initial activity. However, these transition metals are due to multiple valence states such as Fe (Fe)²⁺Or Fe³⁺) The generation of unsaturated coordination surface can lead to the dissolution of metal in electrolyte and the loss of metal ions in the electrochemical reaction process such as Oxygen Reduction Reaction (ORR), thereby reducing the catalytic arc of the material, affecting the purity of the electrolyte, and being not beneficial to the stability of the catalyst and the performance of the electrochemical energy device. The d-orbital of Zn element is a full-filled orbital (3 d) compared with Fe, Co, Ni and Mn₁₀4s₂) Its special electronic structure restricts the formation of ions of higher valence states. From this theoretical point of view, the Zn-N-C catalyst should be more stable than the above-mentioned catalysts. However, Zn-N-C catalysts have been reported to perform in ORR much less than other M-N-C based catalysts such as Fe-N-C. In addition, the preparation of the zinc monatomic catalyst reported at present needs either a high specific surface material (such as CNT) as a carrier or strict high temperature, low temperature rise/fall rate or content of a zinc atom precursor material, the process is relatively complex and uncontrollable, the energy consumption is high, and the subsequent acid/alkali treatment is not beneficial to environmental protection.

Therefore, the existing zinc monoatomic preparation technology still needs to be improved and developed.

Disclosure of Invention

In view of the defects of the prior art, the invention aims to provide a zinc-containing monatomic catalyst, and a preparation method and application thereof, and aims to solve the problems that the preparation process of the existing zinc-containing monatomic catalyst is complex and difficult to control, the energy consumption is high, the post-treatment is not environment-friendly or the stability of the prepared zinc-containing monatomic catalyst is not high.

The technical scheme of the invention is as follows:

a method for preparing a zinc-containing monatomic catalyst, comprising the steps of:

A. heating 2-methylimidazole zinc salt to 80-160 ℃ at a speed of 1-5 ℃/min under a mixed atmosphere of hydrogen and inert gas, calcining for 1-4 h, heating to 200-400 ℃ at a speed of 1-5 ℃/min, calcining for 1-6 h, and heating to 450-750 ℃ at a speed of 2-10 ℃/min, and calcining for 2-5 h to obtain a zinc intermediate;

B. carrying out first mixing treatment on the zinc intermediate and a first alkaline solution or an acidic solution to obtain a first mixed solution, and carrying out solid-liquid separation on the first mixed solution to obtain a first zinc-containing solid; or the like, or, alternatively,

carrying out second mixing treatment on the zinc intermediate and a second alkaline solution to obtain a second mixed solution, carrying out third mixing treatment on the second mixed solution and a metal precursor to be loaded, and carrying out solid-liquid separation on the third mixed solution to obtain a second zinc-containing solid;

C. under the protection of inert gas, heating the first zinc-containing solid or the second zinc-containing solid to 100-160 ℃ at a speed of 1-5 ℃/min, calcining for 2-5 h, heating to 200-400 ℃ at a speed of 1-5 ℃/min, calcining for 2-5 h, and heating to 700-900 ℃ at a speed of 2-10 ℃/min, and calcining for 2-5 h to obtain the zinc-containing monatomic catalyst; the zinc-containing monatomic catalyst is a pure zinc monatomic catalyst or a supported zinc monatomic catalyst.

A zinc-containing monatomic catalyst is prepared by the preparation method.

Use of the above-described zinc-containing monatomic catalyst in an electrochemical redox reaction, wherein the zinc-containing monatomic catalyst is used as a cathode redox catalyst.

Has the advantages that: the method for preparing the zinc-containing monatomic catalyst by using the 2-methylimidazole zinc salt (ZIF8) as the zinc precursor, firstly calcining at low temperature to obtain the zinc intermediate, then etching (and loading) the low-zinc intermediate and finally calcining at high temperature has the following advantages: the process is simple and controllable, the zinc content does not need to be strictly controlled, and a carrier material does not need to be adopted; the low-temperature calcination and etching before the high-temperature calcination can effectively prevent the zinc atoms from agglomerating; the obtained pure zinc monatomic catalyst has good catalytic activity, high stability and better anti-poisoning capability; the obtained loaded zinc-containing monatomic catalyst can further improve the catalytic activity of the pure zinc monatomic catalyst or meet the requirements of different catalytic systems.

Drawings

FIG. 1 is an SEM photograph of ZIF8 used in example 1 of the present invention;

FIG. 2 is an SEM photograph of H-ZIF8 during preparation in example 1 of the present invention;

FIG. 3 shows C-ZIF8-NH during the preparation of example 1 of the present invention₃SEM picture of (1);

FIG. 4 is a drawing showing C-ZIF8-NH prepared in example 1 of the present invention₃-800。

FIG. 5 shows H-ZIF8 and C-ZIF8-NH in example 1 of the present invention₃TEM contrast test of 800: wherein (a) is a TEM image of H-ZIF8, and (b) is C-ZIF8-NH₃A low power TEM image of-800, (C) is C-ZIF8-NH₃High power TEM image of-800.

FIG. 6 is a view showing C-ZIF8-NH in example 1 of the present invention₃-a Selected Area Electron Diffraction (SAED) pattern of 800.

FIG. 7 shows C-ZIF8-NH in example 1 of the present invention₃800 high angle annular dark field image-scanning transmission electron image (HAADF-STEM) maps at different backgrounds.

FIG. 8 shows H-ZIF8 and C-ZIF8-NH in examples 1 to 3 of the present invention₃800, C-ZIF8-NaOH-800 and C-ZIF8-H₂SO₄-800 XRD spectrum contrast.

FIG. 9 shows C-ZIF8-NH in example 5 of the present invention₃-800、C-ZIF8-NaOH-800、C-ZIF8-H₂SO₄LSV curves of-800, ZIF8-800, Pt/C vs. graph.

FIG. 10 shows C-ZIF8-NH in example 5 of the present invention₃-800、C-ZIF8-NaOH-800、C-ZIF8-H₂SO₄Comparative Tafel curves for-800, ZIF8-800, Pt/C.

FIG. 11 is a graph showing C-ZIF8-NH under the condition of constant voltage in example 5 of the present invention₃800, Pt/C versus time.

FIG. 12 is a graph showing the measured C-ZIF8-NH content before and after 20mmol of KSCN in example 5 of the present invention₃-800 ofOxygen reduction LSV curves are compared.

FIG. 13 shows C-ZIF8-NH in example 5 of the present invention₃-800、C-ZIF8-Fe-0.12-800、C-ZIF8-Fe-0.24-800、C-ZIF8-Fe-0.48-800、C-ZIF8-Fe-0.12-750、C-ZIF8-Fe-0.24-900、Fe₃O₄Comparison of oxygen reduction LSV curves for Pt/C.

Detailed Description

The invention provides a zinc-containing monatomic catalyst, a preparation method and an application thereof, and the invention is further described in detail below in order to make the purpose, the technical scheme and the effect of the invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The embodiment of the invention provides a preparation method of a zinc-containing monatomic catalyst, which comprises the following steps:

A. in the mixed atmosphere of hydrogen and inert gas (such as nitrogen, argon and the like), heating the 2-methylimidazole zinc salt to 80-160 ℃ (such as 120 ℃) at 1-5 ℃/min (such as 2 ℃/min) for calcining for 1-4 h (such as 2h and 3h), then heating to 200-400 ℃ (such as 300 ℃) at 1-5 ℃/min (such as 2 ℃/min) for calcining for 1-6 h (such as 2h and 3h), and finally heating to 450-750 ℃ (such as 600 ℃) at 2-10 ℃/min (such as 5 ℃/min) for calcining for 2-5 h (such as 3h) to obtain a zinc intermediate;

C. under the protection of inert gas (such as nitrogen, argon and the like), heating the first zinc-containing solid or the second zinc-containing solid to 100-160 ℃ (such as 120 ℃) at 1-5 ℃/min (such as 2 ℃/min) and calcining for 2-5 h (such as 2h and 3h), then heating to 200-400 ℃ (such as 300 ℃) at 1-5 ℃/min (such as 2 ℃/min) and calcining for 2-5 h (such as 2h and 3h), and finally heating to 700-900 ℃ (preferably 800 ℃) at 2-10 ℃/min (such as 5 ℃/min) and calcining for 2-5 h (such as 3h) to obtain the zinc-containing monatomic catalyst; the zinc-containing monatomic catalyst is a pure zinc monatomic catalyst or a supported zinc monatomic catalyst.

In this embodiment, the method for preparing the zinc-containing monatomic catalyst by using 2-methylimidazole zinc salt (ZIF8) as a zinc precursor, firstly calcining at a low temperature to obtain a zinc intermediate, then etching (and loading) the low-zinc intermediate, and finally calcining at a high temperature has the following advantages: the process is simple and controllable, the zinc content does not need to be strictly controlled, and a carrier material does not need to be adopted; the low-temperature calcination and etching before the high-temperature calcination can effectively prevent the zinc atoms from agglomerating; the obtained pure zinc monatomic catalyst has good catalytic activity, high stability and better anti-poisoning capability; the obtained loaded zinc-containing monatomic catalyst can further improve the catalytic activity of the pure zinc monatomic catalyst or meet the requirements of different catalytic systems.

In one embodiment, in step a, the volume concentration of hydrogen in the mixed atmosphere of hydrogen and inert gas is 10%. The inert gas may be nitrogen or argon, etc.

In one embodiment, in step B, the first alkaline solution can be selected from ammonia water with a concentration of 14 to 28 wt% or NaOH aqueous solution with a concentration of 28 wt%; the acidic solution may be selected from 28 wt% H₂SO₄An aqueous solution.

In one embodiment, in step B, the second alkaline solution is selected from ammonia water with a concentration of 14 to 28 wt%.

In one embodiment, in step B, the metal precursor to be supported is selected from at least one of nitrates, chlorides, or metal-organic compounds of transition metals or noble metals. Further in one embodiment, in step B, the transition metal may be Fe, Co, Mn, Cu or Ni; the noble metal may be Pt, Pd, Ru, Rh or Ag. For example, the metal precursor to be supported may be Fe (NO)₃)₃·9H₂O、FeCl₃、CoCl₂、Co(NO₃)₂Manganese nitrate, manganese chloride, copper nitrate, nickel nitrate, and copper chlorideNickel, palladium chloride, palladium nitrate, platinum chloride, silver nitrate, silver chloride, rhodium nitrate, ruthenium chloride, ruthenium nitrate, and the like, but is not limited thereto.

In one embodiment, in the step B, the ratio of the zinc intermediate to the metal precursor to be loaded is 1g: 1-5 mmol. Preferably, the ratio of the zinc intermediate to the metal precursor to be loaded is 1g: 1.2-2.4 mmol; within the range of the charging proportion, the obtained load type zinc monatomic catalyst has the best electrochemical performance and catalytic activity.

In one embodiment, in step B, the temperature of the first mixing treatment is 25 to 50 ℃ (e.g. room temperature, 30 ℃) for 2 to 48 hours (e.g. 24 hours, preferably 12 to 48 hours); and/or the temperature of the second mixing treatment is 25-50 ℃ (such as room temperature and 30 ℃) for 10-60 min (such as 30 min); and/or the temperature of the third mixing treatment is 25-50 ℃ (such as 30 ℃) for 2-48 h (such as 24h, and the preferable time is 12-48 h).

The embodiment of the invention also provides a zinc-containing monatomic catalyst, wherein the zinc-containing monatomic catalyst is prepared by adopting the preparation method.

Embodiments of the present invention also provide an application of the above-mentioned zinc-containing monatomic catalyst in an electrochemical redox reaction, wherein the zinc-containing monatomic catalyst is used as a cathode oxygen reduction catalyst.

The present invention will be described in detail below with reference to specific examples.

Example 1 pure zinc monatomic catalyst: C-ZIF8-NH₃Preparation of (E) 800

(1) 2-methylimidazole zinc salt (structure:

named as ZIF8) is calcined in a high-temperature tube furnace, and the temperature is raised to 120 ℃ at the speed of 2 ℃/min under the mixed atmosphere of hydrogen and nitrogen, and the temperature is kept for 2 h; and then heating to 300 ℃ at the speed of 2 ℃/min, preserving heat for 2H, finally heating to 600 ℃ at the speed of 5 ℃/min, preserving heat for 3H, and naturally cooling to room temperature to obtain a zinc intermediate which is a gray black powder sample and is named as H-ZIF 8.

(2) Adding H-ZIF8(0.1g) into 10mL of 28 wt% ammonia water, stirring for 24H, filtering, and collecting to obtain a first zinc-containing solid as black sample named C-ZIF8-NH₃。

(3) Under the protection of nitrogen, adding C-ZIF8-NH₃Placing in a high-temperature tube furnace, heating to 120 ℃ at the speed of 2 ℃/min, and keeping the temperature for 2 h; then heating to 300 ℃ at the speed of 2 ℃/min, and preserving heat for 2 h; finally, the temperature is raised to 800 ℃ at the speed of 5 ℃/min, and the temperature is kept for 3h to obtain a black sample which is named as C-ZIF8-NH₃800 is pure zinc monatomic catalyst.

Scanning Electron Microscope (SEM) was used to measure the zinc precursor ZIF8 used in example 1, H-ZIF8 and C-ZIF8-NH during preparation₃And finally prepared C-ZIF8-NH₃800-measured ZIF8 to C-ZIF8-NH₃The topographical variation of-800 is shown in fig. 1-4. The ZIF8 and H-ZIF8 are dodecahedron, so that the dispersibility is good, and the surface structure of a sample calcined by hydrogen mixed gas is not changed; after ammonia water treatment and subsequent carbonization treatment, the product is C-ZIF8-NH₃And C-ZIF8-NH₃800, although the transition to the spherical form has begun and the particle size becomes smaller, the polyhedral structure is still retained.

Transmission Electron Microscope (TEM) was used to measure H-ZIF8 in the preparation of example 1 and C-ZIF8-NH finally obtained₃800, and the test results of H-ZIF8 are shown in FIG. 5(a), C-ZIF8-NH₃The test results of-800 are shown in FIG. 5(b, c), wherein b is a low power TEM image and c is a high power TEM image; and to C-ZIF8-NH₃Selected Area Electron Diffraction (SAED) test was performed at 800, and the results are shown in FIG. 6. It can be seen that C-ZIF8-NH is obtained after etching and calcination at 800 ℃ compared with the regular polygonal structure of H-ZIF8₃800 particles become smaller with some degree of change in shape; although no significant crystal structure was observed for both samples, C-ZIF8-NH₃The electron (light) transmission of-800 was stronger, indicating that C-ZIF8-NH₃More pores are present at 800, indicating that the removal of ZnO and the etching effect of ammonia make C-ZIF8-NH₃800 poresMore highly, this abundance of pores may be more conducive to mass transfer and allow the reaction to proceed in a more catalytic direction. The multi-site amorphous structure carbon material formed by carbonization at 800 ℃ has no obvious lattice stripes, is also shown to form rings through an isolated monatomic SAED image, is a (002) crystal face of C, shows poor crystallinity of the whole carbon skeleton, and further proves that no crystalline Zn species is formed during the heat treatment at 800 ℃.

C-ZIF8-NH prepared in example 1₃800 results of high-angle annular dark field image-scanning transmission electron image (HAADF-STEM) tests under different backgrounds are shown in FIG. 7, it is known that different elements have different contrasts due to different structures, heavy elements show higher brightness, and as shown by circles in the figure, heavy elements Zn are dispersed in a carbon structure almost in a unit point manner and are also uniformly dispersed, and the synthesized sample C-ZIF8-NH is proved₃800 is pure zinc monatomic catalyst.

Example 2 pure zinc monatomic catalyst: preparation of C-ZIF8-NaOH-800

The preparation procedure is the same as in example 1, except that: 10mL of 28 wt% aqueous NaOH solution was used in place of 10mL of 28 wt% aqueous ammonia.

Example 3 pure zinc monatomic catalyst: C-ZIF8-H₂SO₄Preparation of (E) 800

The preparation procedure is the same as in example 1, except that: 10mL of 28 wt% H was used₂SO₄The aqueous solution replaced 10mL of 28 wt% strength aqueous ammonia.

For the H-ZIF8 obtained in the preparation of example 1 and the C-ZIF8-NH obtained in examples 1-3, respectively₃800, C-ZIF8-NaOH-800 and C-ZIF8-H₂SO₄800X-ray diffraction (XRD) tests were carried out, and the results of their tests are shown in FIG. 8. H-ZIF8 was found to contain ZnO; ZnO (the corresponding diffraction peak of PDF: 36-1451) completely disappears after acid or alkali etching, and only the diffraction peak of the amorphous carbon material exists; it is shown that the Zn compound is highly dispersed after etching, thereby highly dispersing Zn in the finally prepared zinc-containing monatomic catalyst.

EXAMPLE 4 preparation of Supported Zinc monatomic catalyst

(1) Calcining ZIF8 in a high-temperature tube furnace, heating to 120 ℃ at a speed of 2 ℃/min under the mixed atmosphere of hydrogen and nitrogen, and preserving heat for 2 h; and then heating to 300 ℃ at the speed of 2 ℃/min, preserving heat for 2H, finally heating to 600 ℃ at the speed of 5 ℃/min, preserving heat for 3H, and naturally cooling to room temperature to obtain a zinc intermediate which is a gray black powder sample and is named as H-ZIF 8.

(2) 0.1g of H-ZIF8 was added to 10mL of 28 wt% ammonia water, and stirring was continued for 30min, after which various amounts of Fe (NO) were added to the reaction flask₃)₃·9H₂O (0.12mmol, 0.24mmol, 0.48mmol), stirring at constant temperature of 30 ℃ for 24h, filtering, separating, and vacuum drying to obtain gray black powder, which are respectively named as C-ZIF8-Fe-0.12, C-ZIF8-Fe-0.0.24, and C-ZIF 8-Fe-0.48. Then obtaining a black powder sample through the calcining process, namely the zinc monatomic supported catalyst.

(3) Under the protection of nitrogen, respectively placing C-ZIF8-Fe-0.12, C-ZIF8-Fe-0.0.24 and C-ZIF8-Fe-0.48 in a high-temperature tube furnace, heating to 120 ℃ at the speed of 2 ℃/min, and preserving heat for 2 hours; then heating to 300 ℃ at the speed of 2 ℃/min, and preserving heat for 2 h; and finally, heating to 800 ℃ at the speed of 5 ℃/min, and preserving heat for 3 hours to obtain the supported zinc monatomic catalyst which is a black sample and is named as C-ZIF8-Fe-0.12-800, C-ZIF8-Fe-0.0.24-800 and C-ZIF8-Fe-0.48-800 respectively.

(4) Under the protection of nitrogen, C-ZIF8-Fe-0.12 is placed in a high-temperature tube furnace, the temperature is raised to 120 ℃ at the speed of 2 ℃/min, and the temperature is kept for 2 h; then heating to 300 ℃ at the speed of 2 ℃/min, and preserving heat for 2 h; and finally, heating to 750 ℃ at the speed of 5 ℃/min, and preserving heat for 3 hours to obtain the supported zinc monatomic catalyst which is a black sample and is named as C-ZIF 8-Fe-0.12-750.

(5) Under the protection of nitrogen, C-ZIF8-Fe-0.24 is placed in a high-temperature tube furnace under the protection of nitrogen, the temperature is raised to 120 ℃ at the speed of 2 ℃/min, and the temperature is kept for 2 h; then heating to 300 ℃ at the speed of 2 ℃/min, and preserving heat for 2 h; and finally, heating to 900 ℃ at the speed of 5 ℃/min, and preserving the heat for 3 hours to obtain the supported zinc monatomic catalyst which is a black sample and is named as C-ZIF 8-Fe-0.24-900.

Comparative example 1 preparation of ZIF8-800

Under the protection of nitrogen, ZIF8 is placed in a high-temperature tube furnace, the temperature is raised to 120 ℃ at the speed of 2 ℃/min, and the temperature is kept for 2 h; then heating to 300 ℃ at the speed of 2 ℃/min, and preserving heat for 2 h; and finally, heating to 800 ℃ at the speed of 5 ℃/min, and preserving the heat for 3 hours to obtain a black sample, which is named as ZIF 8-800.

Example 5 characterization of oxygen reduction catalytic Performance of Zinc-containing monatomic catalyst

(1) Preparing a rotating disk electrode: weighing 5mg of catalyst material, dispersing in 400 μ L of analytical alcohol, adding 100 μ L of Nafion (5 wt%), and performing ultrasonic treatment for at least 30 min; 10 μ L of the dispersion was measured and dropped on an electrode, and the electrode was naturally dried.

(2) Electrode ORR performance test conditions and system: the scan was carried out at a rate of 5mV/s in a 0.1M KOH electrolyte at a rate of 1600raps over a voltage range of 0.171 to 1.165V (vs. RHE).

(3) C-ZIF8-NH prepared according to the test procedures and conditions described above for examples 1-3, respectively₃-800、C-ZIF8-NaOH-800、C-ZIF8-H₂SO₄800, ZIF8-800 of comparative example 1, and Pt/C were tested and their LSV (Linear sweep voltammetry) curves compared as shown in FIG. 9. Known as C-ZIF8-NH₃800 has the best performance at the starting voltage (E)_onset) Above, with NH₃The treated sample (1.12V) was higher than the strong bases NaOH (1.09V) and H₂SO₄The treated samples (1.068V), all higher than the E of commercial Pt/C_onset(1.01V); in terms of half-wave potential, E_1/2,NH3(0.861V)≈E_1/2,Pt/C>E_1/2,NaOH(0.8V)>E_1/2,H2SO4(0.73V) is far superior to the one-step direct calcination of the sample ZIF 8-800.

(4) The Tafel slope of the electrochemical reaction is a main evaluation index for reflecting the power speed of electrochemical kinetics, and the larger the Tafel slope is, the slower the reaction kinetics is, and the smaller the slope value is, the faster the catalytic kinetics is.

C-ZIF8-NH prepared in examples 1 to 3, respectively, was measured₃-800、C-ZIF8-NaOH-800、C-ZIF8-H₂SO₄Comparative results of Tafel curves of-800, ZIF8-800 of comparative example 1, and Pt/C are shown in FIG. 10. It is known that C-ZIF8-800 has a higher tafel slopeThe rate (122.59mV/dec) indicates that the redox reaction of the direct carbonization ZIF8 is slow, and the problems of insufficient active sites and the like can exist. C-ZIF8-NH₃The Tafel slope of-800 (84.36mV/dec) is significantly lower than the commercial Pt/C (94.8mV/dec) and also significantly lower than the Tafel slope of the other samples, indicating that the ammonia-treated catalyst material enhances charge transfer kinetics.

(5) According to the stability test method recommended by the Department of Energy (DOE), a catalyst (C-ZIF 8-NH) was tested in a 0.1M KOH solution at a constant potential of 0.79V using a chronoamperometry₃-800) stability: measuring C-ZIF8-NH₃The current holding relative value under the constant voltage cycling condition of-800 Pt/C versus the time of use is shown in FIG. 11. It is known that pure zinc monatomic catalyst C-ZIF8-NH₃The end of the test at a current retention relative value of 97.22% at 800 cycles at constant voltage, much higher than the current retention relative value of commercial Pt/C (63.28%) under the same test conditions; the fully-filled 3d electron orbital property of Zn is responsible for the excellent coordination resistance and reduced redox dissolution of the monatomic catalyst material.

(6) Before and after 20mmol of KSCN is added, pure zinc monatomic catalyst C-ZIF8-NH₃The oxygen reduction LSV curve comparison of-800 is shown in FIG. 12. It was found that the limiting current of the half-wave potential (inject KSCN) at which 20mmol of KSCN was added was reduced by 0.365mA/cm, compared with the half-wave potential (initial) at which KSCN was not added²The half-wave potential is shifted to the left by 15.8mV, and the performance degradation is lower, which indicates that metal (Zn) ions of the material are not the main active sites of the material, and indirectly indicates that zinc exists in a form of a single-atom catalyst and is used for adjusting the electronic structure of adjacent carbon atoms.

(7) The procedure and conditions of examples (1) and (2) were followed to test C-ZIF8-NH prepared in example 1₃800, C-ZIF8-Fe-0.12-800, C-ZIF8-Fe-0.24-800, C-ZIF8-Fe-0.48-800, C-ZIF8-Fe-0.12-750, C-ZIF8-Fe-0.24-900, and conventional Fe prepared in example 4₃O₄Comparison of oxygen reduction LSV curves for Pt/C is shown in FIG. 13. It is known that when the iron precursor (Fe (NO)₃)₃·9H₂O) was charged in an amount of 0.12mmol and 0.24mmol (0.1g of H-ZIF 8),and the calcination temperature is 800 ℃ to have the best electrochemical performance. Half-wave potential E of C-ZIF8-Fe-0.24-800_1/20.90V (vs RHE), limiting Current Density J_lim＝5.44mA/cm²An initial voltage E_onsetActivity was clearly comparable to commercial Pt/C catalyst at 1.15V: e_1/2＝0.851V、J_lim＝4.69mA/cm²And E_onsetThe higher than 1.013V indicates that the catalyst performance is improved well when a trace amount of iron is introduced. Both too high and too low Fe content and calcination temperature are detrimental to the expression of oxygen reduction activity; the performance is far higher than that of a zinc monatomic catalyst and pure Fe₃O₄The compound, and therefore the pure zinc monatomic catalyst, also exhibits a good support effect.

In conclusion, the invention provides a zinc-containing monatomic catalyst, and a preparation method and application thereof. The method for preparing the zinc-containing monatomic catalyst by using the 2-methylimidazole zinc salt (ZIF8) as the zinc precursor, firstly calcining at low temperature to obtain the zinc intermediate, then etching (and loading) the low-zinc intermediate and finally calcining at high temperature has the following advantages: the process is simple and controllable, the zinc content does not need to be strictly controlled, and a carrier material does not need to be adopted; the low-temperature calcination and etching before the high-temperature calcination can effectively prevent the zinc atoms from agglomerating; the obtained pure zinc monatomic catalyst has good catalytic activity, high stability and better anti-poisoning capability; the obtained loaded zinc-containing monatomic catalyst can further improve the catalytic activity of the pure zinc monatomic catalyst or meet the requirements of different catalytic systems.

It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.

Claims

1. A preparation method of a zinc-containing monatomic catalyst is characterized by comprising the following steps:

2. The method according to claim 1, wherein in the step a, the volume concentration of hydrogen in the mixed atmosphere of hydrogen and inert gas is 10%.

3. The preparation method according to claim 1, wherein in the step B, the first alkaline solution is selected from ammonia water with a concentration of 14-28 wt% or NaOH aqueous solution with a concentration of 28 wt%; the acidic solution is selected from H with a concentration of 28 wt%₂SO₄An aqueous solution.

4. The method according to claim 1, wherein in the step B, the second basic solution is selected from ammonia water having a concentration of 14 to 28 wt%.

5. The production method according to claim 1, wherein in step B, the metal precursor to be supported is selected from at least one of a nitrate, a chloride, or a metal organic compound of a transition metal or a noble metal.

6. The production method according to claim 5, wherein in step B, the transition metal is Fe, Co, Mn, Cu or Ni; the noble metal is Pt, Pd, Ru, Rh or Ag.

7. The preparation method according to claim 1, wherein in the step B, the ratio of the zinc intermediate to the metal precursor to be loaded is 1g: 1-5 mmol.

8. The preparation method according to claim 1, wherein in the step B, the temperature of the first mixing treatment is 25-50 ℃ and the time is 2-48 h; and/or the temperature of the second mixing treatment is 25-50 ℃, and the time is 10-60 min; and/or the temperature of the third mixing treatment is 25-50 ℃, and the time is 2-48 h.

9. A zinc-containing monatomic catalyst, characterized by being produced by the production method according to any one of claims 1 to 8.

10. Use of a zinc-containing monatomic catalyst according to claim 9 as a cathodic oxygen reduction catalyst in an electrochemical redox reaction.