阅读说明：本技术 一种二维超薄金属有机框架纳米片电催化剂、其制备方法及应用 (Two-dimensional ultrathin metal organic framework nanosheet electrocatalyst, and preparation method and application thereof ) 是由 侯阳 寇振辉 杨彬 雷乐成 于 2020-12-30 设计创作，主要内容包括：本发明涉及能源材料合成技术领域,公开一种二维超薄金属有机框架纳米片电催化剂、其制备方法及应用,该催化剂的制备方法包括步骤：将氯化铵、氮源、均苯四甲酸酐、四水合钼酸铵和过渡金属盐混合研磨,经煅烧、洗涤、干燥得到具有金属有机框架结构的催化剂；再将其作为负极,进行电化学剥离,再液相超声分散,再离心、冷冻干燥,得到二维超薄金属有机框架纳米片电催化剂。本发明通过采用电化学剥离和液相超声辅助剥离相结合,使得金属有机框架纳米片催化剂暴露出更多的反应活性位点,表现出很高的催化活性和稳定性,明确的催化活性中心促进了电催化析氧反应。(The invention relates to the technical field of energy material synthesis, and discloses a two-dimensional ultrathin metal organic framework nanosheet electrocatalyst, a preparation method and application thereof, wherein the preparation method of the catalyst comprises the following steps: mixing and grinding ammonium chloride, a nitrogen source, pyromellitic dianhydride, ammonium molybdate tetrahydrate and transition metal salt, calcining, washing and drying to obtain a catalyst with a metal-organic framework structure; and then the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst is used as a negative electrode, subjected to electrochemical stripping, subjected to liquid-phase ultrasonic dispersion, centrifuged, and freeze-dried to obtain the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst. According to the invention, by combining electrochemical stripping and liquid-phase ultrasonic-assisted stripping, more reaction active sites are exposed out of the metal organic framework nanosheet catalyst, high catalytic activity and stability are shown, and an electrocatalytic oxygen evolution reaction is promoted by a specific catalytic activity center.)

1. A preparation method of a two-dimensional ultrathin metal organic framework nanosheet electrocatalyst is characterized by comprising the following steps:

(1) mixing and grinding ammonium chloride, a nitrogen source, pyromellitic dianhydride, ammonium molybdate tetrahydrate and transition metal salt, calcining, washing and drying to obtain a catalyst with a metal-organic framework structure;

(2) taking the catalyst prepared in the step (1) as a negative electrode and platinum as a positive electrode, carrying out electrochemical stripping in a quaternary ammonium salt solution, and collecting precipitates in an electrolyte;

(3) and placing the collected precipitate in an organic solvent for ultrasonic dispersion, centrifuging, and freeze-drying to obtain the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst.

2. The method of preparing a two-dimensional ultra-thin metal-organic framework nanosheet electrocatalyst according to claim 1, wherein the nitrogen source comprises urea; the transition metal salt comprises any one or more of soluble salts of iron, cobalt, nickel, manganese and alloys thereof.

3. A preparation method of a two-dimensional ultrathin metal organic framework nanosheet electrocatalyst according to claim 1, wherein the mass ratio of the ammonium chloride, the nitrogen source, the pyromellitic anhydride, the ammonium molybdate tetrahydrate and the transition metal salt is 18-22: 80-85: 40-45: 1: 15-30.

4. The preparation method of the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst according to claim 1, wherein in step (1), the calcination temperature is 220-280 ℃ and the calcination time is 3-5 h.

5. The method of preparing a two-dimensional ultra-thin metal organic framework nanosheet electrocatalyst according to claim 1, wherein the quaternary ammonium salt comprises any one of tetrapropylammonium chloride, tetrabutylammonium bromide, tetraheptylammonium bromide; the solvent in the solution of the quaternary ammonium salt is any one of acetonitrile, acetone, water, isopropanol and propylene carbonate.

6. The preparation method of the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst according to claim 1, wherein in the step (2), the applied voltage for electrochemical stripping is 10-20V, and the stripping time is 1-3 h.

7. The preparation method of the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst according to claim 1, wherein in step (3), the ultrasonic power is 320-500W, and the ultrasonic time is 8-12 h; the organic solvent comprises acetonitrile and/or acetone.

8. The preparation method of the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst according to claim 1, wherein in the step (3), the centrifuging comprises low-speed centrifuging and high-speed centrifuging, and the rotating speed of the low-speed centrifuging is 1500-2000 r/min; the rotating speed of the high-speed centrifugation is 8000-10500 r/min; the freeze drying treatment time is 24-48 h.

9. A two-dimensional ultrathin metal organic framework nanosheet electrocatalyst prepared according to the preparation method of any one of claims 1 to 8.

10. The use of a two-dimensional ultrathin metal-organic framework nanosheet electrocatalyst according to claim 9 as an anode material in an electrocatalytic water splitting reaction.

Technical Field

The invention relates to the technical field of energy material synthesis, in particular to a two-dimensional ultrathin metal organic framework nanosheet electrocatalyst, and a preparation method and application thereof.

Background

In recent years, with the increasing progress of science and technology and the rapid development of economy, most industrial production processes consume non-renewable fossil energy mainly comprising coal, petroleum, natural gas and the like. Along with the acceleration of development pace, coal reserves are continuously reduced, the oil exploitation amount is continuously increased, and the phenomenon of short supply and short demand of natural gas also occurs. As the most developing countries, China takes raw coal as a main energy structure, so that the environmental pollution problem is particularly prominent. At present, various countries in the world vigorously develop environment-friendly renewable new energy sources for replacing traditional non-renewable energy sources. Among the new energy sources, hydrogen energy has a value of 14.3 × 10 because of its renewable energy sources, such as solar energy, wind energy, biomass energy, geothermal energy, etc⁷The characteristics of extremely high calorific value of J/kg, greenness, no pollution, wide utilization range, easy storage and the like are widely concerned by scientists all over the world.

Current methods for producing hydrogen can be divided into three categories depending on the source of the feedstock: hydrogen production by fossil fuel, biological hydrogen production and hydrogen production by water cracking. The electrocatalytic water splitting hydrogen production is slightly limited by uncertain factors such as electric power, regions and the like, and is an effective way for producing clean and pollution-free hydrogen energy which is developed rapidly in recent years. However, there are some scientific problems to be solved in the reaction process of water electrolysis, such as that the slow kinetic characteristics of the anodic Oxygen Evolution Reaction (OER) caused by its complicated four-electron process in the water electrolysis process have become bottlenecks that restrict the overall efficiency of the water electrolysis reaction, thereby limiting the large-scale development and application of water electrolysis.

So far, researchers have conducted intensive studies on the mechanism of electrochemically decomposing water, and have conducted all-around construction and modification of the corresponding catalyst. Catalysts as currently studied include four broad classes of noble metal catalysts, transition metal catalysts, non-metal catalysts, and molecular catalysts. The noble metal catalyst comprises iridium (Ir) base, platinum (Pt) base and other materials, has excellent electrocatalytic water cracking performance and has the advantages of nearly zero hydrogen adsorption free energy, high catalytic activity and the like, but can not realize large-scale application due to the factors of low reserve content, high cost, poor stability in reaction and the like; also each of the other three classes of catalysts has its own advantages and disadvantages. Therefore, a catalyst material with good catalytic activity and good stability in the reaction process needs to be developed, the discovery of the single-layer graphene in 2004 raises the hot trend of research on two-dimensional functional materials, and the two-dimensional materials enable the realization of efficient electrocatalytic reaction instead of commercial Pt/C catalysts. At present, the strategies for improving the reaction activity of the catalytic material mainly include: 1) performing edge engineering; 2) defect engineering; 3) crystal phase engineering; 4) atom doping and surface stress; 5) and (3) a composite structure. For this reason, Metal Organic Framework (MOF) materials having a two-dimensional structure have been developed by researchers due to their advantages such as high porosity, structural diversity and surface structure adjustability.

For example: chinese patent publication No. CN111790448A discloses a composite material with ZIF-9(III)/CoLDH nanosheets and a preparation method thereof. Respectively dispersing cobalt salt and benzimidazole in an N, N-dimethylformamide solvent, carrying out reflux reaction at a certain temperature for a period of time, finally cooling to room temperature, and then carrying out centrifugation, washing and drying to obtain ZIF-9 (I); mixing and dissolving ZIF-9(I) and cobalt salt in a mixed solvent of absolute ethyl alcohol and ultrapure water, carrying out reflux reaction, and then carrying out centrifugal separation, washing and drying treatment to obtain the ZIF-9(III)/Co LDH composite material with the nanosheet morphology. However, the stacking condition of the nano flaky ZIF-9(III)/Co LDH composite material is serious, so that a good space structure is lacked, and an active site cannot be fully exposed, so that the oxygen evolution performance of water generated by electrocatalytic cracking is poor.

Also, for example, chinese patent publication No. CN110655654A discloses a method for preparing a two-dimensional layered Co-MOF electrode material, which comprises adding terephthalic acid to a mixed solution of N, N-dimethylformamide, ethanol and deionized water, adding cobalt acetate tetrahydrate, transferring the mixed solution to a hydrothermal kettle, cooling to room temperature, centrifuging, washing, and drying. For the electrocatalytic cracking water oxygen evolution reaction, Co-MOF electrolysisThe electrode material is 10mA/cm²The overpotential at 47mV, significantly lower than 730mV for Cu-MOF, but there is still some gap compared to commercial platinum carbon (40 wt% Pt/C) catalysts with good oxygen evolution performance. Therefore, the development and development of the ultrathin two-dimensional metal organic framework electrocatalyst which has large specific surface area, clear active center, clear coordination structure and easy large-scale preparation becomes a problem which needs to be solved urgently at present.

Disclosure of Invention

The invention aims to overcome the defects that the electrocatalytic cracking water oxygen evolution catalyst in the prior art is insufficient in activity and not easy to prepare in a large scale, and provides a preparation method of a two-dimensional ultrathin metal organic framework nanosheet electrocatalyst.

In order to achieve the purpose, the invention adopts the technical scheme that:

a preparation method of a two-dimensional ultrathin metal organic framework nanosheet electrocatalyst comprises the following steps:

(1) mixing and grinding ammonium chloride, a nitrogen source, pyromellitic dianhydride, ammonium molybdate tetrahydrate and transition metal salt, calcining, washing and drying to obtain a catalyst with a metal-organic framework structure;

(2) taking the catalyst prepared in the step (1) as a negative electrode and platinum as a positive electrode, carrying out electrochemical stripping in a quaternary ammonium salt solution, and collecting precipitates in an electrolyte;

(3) and placing the collected precipitate in an organic solvent for ultrasonic dispersion, centrifuging, and freeze-drying to obtain the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst.

The principle of the preparation method of the invention is as follows: the transition metal ions and pyromellitic anhydride form a transition metal-based poly-phthalocyanine structure, and the site which is dominant in oxygen evolution reaction activity is a metal-tetranitrogen structure (M-N)₄)，M-N₄The structure is located in a conjugated plane for condensing four aromatic rings, and the transition metal ions pass through two common cavities in the conjugated planeThe invention provides a method for intercalating and then stripping a metal organic framework nanosheet material by an electrochemical method, wherein quaternary ammonium salt is used for intercalating the metal organic framework nanosheet material, the layer-to-layer distance of the metal organic framework nanosheet material is enlarged, and then the metal organic framework nanosheet material is dispersed in a specific solvent, so that the metal organic framework nanosheet material can meet and balance the energy consumed by stripping the metal organic framework nanosheet material, and then the multilayer metal organic framework nanosheet is directly stripped into a single-layer or few-layer ultrathin two-dimensional metal organic nanosheet framework nanosheet by the energy of surface ultrasonic waves. The main catalytic action on the electrocatalytic water-splitting oxygen evolution reaction is active sites which are formed by dispersing transition metal atoms in a conjugated aromatic network of phthalocyanine rings and are exposed at high density in the stripped few-layer or single-layer metal organic framework nanosheets.

According to the invention, the two-dimensional ultrathin metal organic framework nanosheet catalyst is prepared by combining electrochemical stripping and liquid-phase ultrasonic-assisted stripping, so that the metal organic framework nanosheet catalyst has the characteristics of exposing more reaction active sites, good coordination environment, uniform reaction center and the like, shows very high catalytic activity and stability, and the specific catalytic activity center promotes the electrocatalytic oxygen evolution reaction.

Meanwhile, in the step (3), in the electrochemical stripping process, the catalyst with the metal-organic framework structure prepared at the early stage must be placed on the negative electrode, and cations used in the cation intercalation process comprise: li⁺、 Na⁺、K⁺、TBA⁺、THA⁺、TPA⁺And the like, the interlayer spacing is mainly enlarged in the cathode intercalation process, the large-size ultrathin 2D nanosheet with a complete crystal phase structure can be generated, the electronic structure and the like of the ultrathin 2D nanosheet cannot be irreversibly damaged, and the ultrathin 2D nanosheet can be better used in electrocatalysis application. The electrochemical stripping method is generally adopted to prepare the ultrathin 2D material, and two methods are generally included: anion intercalation and cation intercalation to make stacked lamellar materialAnd the film falls off to form an ultrathin 2D nanosheet. Anions generally used include: SO (SO)₄ ^2-、 OH^-、Cl^-、Br^-、I^-、ClO^4-、BF^4-、PF^4-And so on. The inventor discovers in the research that when the catalyst is used as a positive electrode, the whole stripping efficiency can be greatly improved when anion intercalation is used, but the stripping process mainly depends on the fact that the material is close to the edge of the material in an electrolyte by means of anions, the interlayer spacing of the material is gradually opened from the material boundary after surface oxidation occurs, the material is forced to have the stripping action, but the method can cause a large number of defects to appear on the surface of the material, and the electronic structure and the like of the material can be irreversibly and seriously damaged, so that the application of the material in the relevant aspects is influenced.

The nitrogen source comprises urea; the transition metal salt comprises any one or more of soluble salts of iron, cobalt, nickel, manganese and the like and alloys thereof.

Preferably, the transition metal salt comprises ferric chloride, nickel chloride hexahydrate, cobalt chloride hexahydrate, a mixture of any one or more thereof.

The mass ratio of the ammonium chloride to the nitrogen source to the pyromellitic dianhydride to the ammonium molybdate tetrahydrate to the transition metal salt is 18-22: 80-85: 40-45: 1: 15-30.

In the step (1), the calcining temperature is 220-280 ℃, and the calcining time is 3-5 h.

After calcination, washing is carried out by sequentially washing with ethanol, water and acetone to remove redundant impurities and the like, drying aims at removing washing solvent, water and the like, and vacuum drying can be carried out for 8-12 h at the temperature of 60-80 ℃.

Generally, for electrochemical stripping, two methods of anions and cations can be adopted for common stripping, namely, the whole stripping efficiency can be greatly improved when anion intercalation is used, but the stripping process mainly depends on that the material is close to the edge of the material by means of anions in electrolyte, the interlayer spacing of the material is gradually opened from the material boundary after surface oxidation occurs, and the material is forced to be stripped, but the method can cause a large number of defects to appear on the surface of the material, the electronic structure and the like of the material can be irreversibly and seriously damaged, the application of the material in related aspects is influenced, and the like, but the catalyst of the metal organic framework structure explored in the invention, if the type of the adopted stripping agent is improper, the metal organic framework structure is damaged or changed, and the catalytic activity is lost, the method of cathode stripping is adopted, the quaternary ammonium salt cation is effectively inserted between nanosheets of the metal organic framework structure, the interlayer spacing is expanded, and irreversible damage to a crystalline phase structure, an electronic structure and the like is avoided, so that the material has more excellent performance in electrocatalysis application. Therefore, the electrochemical stripping of the MOF catalyst is a very challenging task, because the related structure of the material and the like are easily changed in the electrochemical stripping process, ultrathin nanosheets with undamaged structures are obtained by electrochemical stripping under the efficient condition, and the selection of the stripping electrolyte and the selection of the related stripping parameters are very important.

Preferably, the quaternary ammonium salts include tetrapropylammonium chloride, tetrabutylammonium bromide, and tetraheptylammonium bromide. Other quaternary ammonium salts such as tetramethylammonium chloride, tetramethylammonium bromide, tetraethylammonium chloride and the like are not recommended to be used, because the MOF catalyst is stripped in the solvent, the stripping action can be generated, the time consumption is long, the energy loss is large, and the stripped MOF catalyst is difficult to prepare ultrathin 2D nanosheets.

The solvent in the solution of the quaternary ammonium salt can be acetonitrile, acetone, water, isopropanol, Propylene Carbonate (PC) and the like. Preferably, the solvent in the solution of the quaternary ammonium salt is acetonitrile. Different quaternary ammonium salts are dissolved in other solvents except acetonitrile, when the same voltage is applied to the solution for intercalation stripping, the conductivity of the corresponding solution is very poor, the excellent conductivity cannot be improved like the acetonitrile solvent to carry out intercalation stripping on the MOF catalyst, the current shown by other solvents is very small under the same voltage, the quaternary ammonium salts cannot be effectively inserted between the MOF catalyst layers, and the stripping efficiency is poor.

The mass concentration of the quaternary ammonium salt in the quaternary ammonium salt solution is 1-5 mg/mL.

In the step (2), the applied voltage for electrochemical stripping is 10-20V, and the stripping time is 1-3 h. When different voltages are applied for stripping, such as 10V, 12V and 15V, the stripping efficiency is low, the intercalation process cannot be effectively carried out, and the yield is low. The stripping time is short, the intercalation is insufficient, namely, the stripped material obtained in the step cannot be effectively and sufficiently dispersed into ultrathin 2D nanosheets in the subsequent ultrasonic dispersion process. Therefore, applying proper voltage and time to the electrochemical stripping MOF catalyst is very important for efficiently obtaining the ultrathin 2D MOF nanosheet catalyst.

In the step (3), the ultrasonic power is 320-500W, and the ultrasonic time is 8-12 h; the purpose of ultrasonic treatment is to further disperse the electrochemically stripped catalyst to form a nano flaky structure, and the catalyst can be directly scattered into powder when the ultrasonic power is too high.

In the step (3), the organic solvent includes acetonitrile and/or acetone. There were 8 solvents tried: acetonitrile, ethanol, isopropanol, methanol, water, N-Dimethylformamide (DMF), N-dimethylacetamide and acetone. Among them, acetonitrile, isopropanol, water, acetone and methanol are preferred. The effect of different solvents on the results was: the solvent with good effect can well disperse the material, so that more appropriate surface tension is provided for the 2D material, and the dispersed 2D material dispersion liquid can be maintained for a long time without precipitation, so that the 2D material is effectively prevented from re-agglomeration; less effective solvents do not provide adequate surface tension and tend to agglomerate in the dispersion in a short time and precipitate.

In the step (3), the centrifugation comprises low-speed centrifugation and high-speed centrifugation, wherein the rotation speed of the low-speed centrifugation is 1500-2000 r/min; the rotating speed of the high-speed centrifugation is 8000-10500 r/min; the freeze drying treatment time is 24-48 h. The low-speed centrifugation aims to discard the sediment centrifuged at the rotating speed, namely the nanosheets which are not well stripped and have serious multilayer stacking conditions, and only retain the supernatant containing few layers or single-layer nanosheets successfully stripped; freeze-drying to obtain a powder sample of few-layer or single-layer nanosheets in the dispersion obtained in the step, and carrying out electrocatalysis performance testing and related characterization work.

The invention also provides a two-dimensional ultrathin metal organic framework nanosheet electrocatalyst prepared according to the preparation method. The catalyst has an ultrathin nanosheet structure, retains the structure of a metal organic framework, has a plurality of reactive sites, and has a good coordination structure and a uniform reaction center.

The invention also provides application of the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst as an anode material in electrocatalytic water cracking reaction, the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst has high catalytic activity and stability, has small overpotential and low Tafel slope, and has no great change in electrocatalytic activity after long-time multiple cycle tests.

Compared with the prior art, the invention has the following beneficial effects:

at present, electrochemical stripping is mainly applied to structures such as sulfide and graphene to prepare a nano flaky structure, and a catalyst with a metal organic framework structure is not reported in a mature way.

On the other hand, the preparation method is simple, low in cost, high in controllability and very suitable for large-scale popularization and industrial production.

Drawings

FIG. 1 is a TEM image of a two-dimensional ultrathin metal-organic framework nanosheet catalyst prepared in example 1;

FIG. 2 is an XRD pattern of a two-dimensional ultrathin metal organic framework nanosheet catalyst prepared in examples 1-4;

FIG. 3 is a LSV curve chart of catalysts prepared by examples 1-4 in application example 1 and comparative example 1;

FIG. 4 is a graph of the Tafel slope for catalysts prepared using examples 1-4 of application example 1 and comparative example 1;

fig. 5 is a graph of electrochemical stability test of the catalyst prepared in example 1 of application example 2.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Those skilled in the art should understand that they can make modifications and equivalents without departing from the spirit and scope of the present invention, and all such modifications and equivalents are intended to be included within the scope of the present invention.

Example 1

(1) Grinding and mixing ammonium chloride, urea, pyromellitic dianhydride, ammonium molybdate tetrahydrate, nickel chloride hexahydrate and ferric chloride according to the mass ratio of 20:82:42:1:24:12 until the mixture is uniformly formed; raising the temperature of the mixture from room temperature to 240 ℃ in a tube furnace, keeping the temperature and calcining for 3h, and cooling the mixture to room temperature along with the furnace; the calcined mixture is washed repeatedly by water, acetone and ethanol in sequence, and each solvent can be washed repeatedly in the washing process, so that impurities such as salts and the like in the MOF synthesis process can be removed completely; after washing, placing the mixture in a vacuum drying environment at 80 ℃ for 12h to obtain a catalyst with a metal organic framework structure;

(2) adopting a tetraheptyl ammonium bromide solution with the concentration of 5.0mg/mL as electrolyte, bonding the metal organic framework nanosheet catalyst prepared in the step (1) on conductive copper through conductive silver paint, fixing the metal organic framework nanosheet catalyst by using an electrode clamp as a cathode of an electrochemical cell, taking a Pt sheet electrode as an anode, applying a voltage of +20V for 2h, and collecting precipitates in the electrolyte to obtain a product after intercalation;

(3) ultrasonically oscillating the collected precipitate in an acetonitrile solvent for 12h, wherein the ultrasonic power is 500W; centrifuging the dispersion liquid after ultrasonic treatment at 2000r/min, taking supernatant, centrifuging the supernatant at 10000r/min, collecting precipitate, and freeze-drying for 24h to obtain the two-dimensional ultrathin metal organic framework nanosheet electrocatalyst.

The two-dimensional ultrathin metal organic framework nanosheet electrocatalyst prepared in example 1 is subjected to a TEM test, and the microstructure of the nanosheet electrocatalyst is observed, as shown in fig. 1, it can be seen that the ultrathin catalyst with a lamellar structure obtained by the method of this example can also be found by observing an XRD spectrum, and after the MOF catalyst is stripped, two characteristic peaks (about 20 ℃ and 30 ℃) which correspond to the most obvious MOF catalyst basically disappear, which can also indicate that the stripping is successful.

Example 2

According to the preparation process of the example 1, the electrolyte in the step (2) is replaced by a tetrapropylammonium chloride solution of 5.0mg/mL, and other steps are unchanged.

Example 3

According to the preparation process of the example 1, the electrolyte in the step (2) is replaced by a tetrabutylammonium chloride solution of 5.0mg/mL, and other steps are unchanged.

Example 4

According to the preparation process of example 1, the electrolyte in step (2) was replaced with 5.0mg/mL tetrabutylammonium bromide solution, and the other steps were unchanged.

Comparative example 1

The catalyst prepared in step (1) of example 1 was used as comparative example 1, and the peeling processes of steps (2) and (3) were not performed.

Comparative example 2

According to the preparation process of the embodiment 1, other processes are not changed, in the step (2), the metal organic framework nanosheet catalyst prepared in the step (1) is adhered to conductive copper through conductive silver paint, the conductive silver paint is fixed by an electrode clamp to be used as an anode of an electrochemical cell, a Pt thin sheet electrode is used as a cathode, 1.0M ammonium sulfate/sodium sulfate/potassium sulfate/sulfuric acid is used as electrolyte, and a certain voltage is applied to strip the metal organic framework nanosheet catalyst. After stripping treatment for a certain time, the metal organic framework nanosheet catalyst is found not to fall off in the electrolyte.

Comparative example 3

According to the preparation process of the embodiment 1, under the condition that other preparation processes are not changed, in the step (2), the voltage is applied to 10V, 12V and 15V for carrying out the intercalation stripping process;

according to the preparation process of the embodiment 1, in the step (3), the ultrasonic power can be changed into 320W, 360W and 400W, and the ultrasonic time can be changed into 2h, 4h, 6h and 8h to perform the ultrasonic dispersion treatment process on the metal organic framework nanosheet;

after the parameters of the applied voltage of electrochemical stripping are changed, the phenomena of reduced stripping efficiency or insufficient stripping efficiency and the like can occur, so that quaternary ammonium salt ions cannot be effectively inserted into the metal organic framework nanosheet layers to expand the interlayer spacing, and the preparation of the few-layer or single-layer 2D metal organic framework nanosheet catalyst is influenced; the change of ultrasonic power and ultrasonic time can cause the occurrence of incomplete stripping, and the dispersion liquid only has a small amount of monolayer or ultrathin metal organic framework nanosheets, which shows that the dispersion liquid can generate a precipitation phenomenon in a short time.

Performance testing

XRD tests are carried out on the catalysts prepared in examples 1-4 and comparative example 1, the crystal structures of the catalysts are observed, and as shown in figure 2, the metal organic framework catalyst of comparative example 1 which is not stripped mainly corresponds to the peaks at the temperature of 20 ℃ and the temperature of 30 ℃, and the peaks at the temperature of 20 ℃ and the temperature of 30 ℃ of examples 1-4 which are electrochemically stripped basically disappear, which shows that the morphology of the multilayer stack is changed into a few-layer or single-layer structure after the electrochemical stripping process.

Application example 1

The catalysts prepared in the embodiments 1-4 and the comparative example 1 are applied to an electro-catalytic water cracking oxygen evolution reaction, Ag/AgCl is used as a reference electrode, a graphite electrode is used as a counter electrode, the prepared ultrathin metal organic framework nanosheet is used as a working electrode, and 1.0M potassium hydroxide is used as an electrolyte solution to jointly form a three-electrode system;

cyclic Voltammetry (CV) activation was performed using the shanghai chen CHI 660E electrochemical workstation: before the test, nitrogen gas was continuously introduced into the electrolyte for 30 min. And (3) adopting a CV program, wherein the test interval is 0-0.8V vs. Ag/AgCl, the sweep speed is 50mV/s, and the electrode is circulated for 40 circles to reach a stable state.

And (3) performing Linear Sweep Voltammetry (LSV) test, switching to an LSV program after electrode activation, wherein the test interval is 0-0.8V vs. Ag/AgCl, and the sweep rate is 5 mV/s. The LSV curve chart of the electrocatalytic oxygen evolution reaction of the electrocatalysts prepared in the examples 1-4 and the comparative example 1 is shown in FIG. 3.

Metal organic framework nanosheet catalyst prepared in example 1, at 10mA cm^-2Has a smaller overpotential (330mV) with a value smaller than that of an Ir/C electrode (350 mV). The potential of example 2 was 470mV, the potential of example 3 was 370mV, the potential of example 4 was 410mV, and the overpotential of comparative example 1, as seen in FIG. 3, was at 10mA cm^-2The current density of the catalyst is far higher than that of the catalyst in the embodiment 1-4, which shows that the metal organic framework nanosheet catalyst stacked in layers is successfully separated into the few-layer or single-layer ultrathin 2D metal organic framework nanosheet electrocatalyst through a reasonable electrochemical stripping process, so that more active sites are exposed out of the catalyst, and the catalytic performance is obviously improved.

The tafel slope plots of the electrocatalysts prepared in examples 1-4 and comparative example 1 are shown in fig. 4, which shows that the catalytic performance of the catalyst prepared in example 1 is far superior to that of comparative example 1, corresponding to the potential results of fig. 3.

Application example 2

And (3) stability testing: for example, in application example 1, the catalyst prepared in example 1 is applied to an electrocatalytic water-splitting oxygen evolution reaction, and the program is switched to a V-t program during testing, and the current density is 10mA cm^-2Under the conditions, the stability of the catalyst was tested and the time was set at 280000 s. The graph of the change of voltage with time is shown in fig. 5, and it can be seen that the potential of the metal organic framework nanosheet catalyst prepared in example 1 is not obviously reduced under the action of a long time, which proves that the catalyst has good electrochemical stability.