Monatomic metal catalyst, method for preparing the same, and use thereof

Abstract

The application relates to the technical field of single-atom catalysis, and provides a single-atom metal catalyst and a preparation method and application thereof, which comprises the following steps: vacuum thermal evaporation is adopted to evaporate a metal layer on a carbon film to obtain a substrate, then vacuum thermal evaporation is continuously adopted to evaporate n times on the substrate, a layer structure obtained by previous evaporation is used as a substrate for the next evaporation, metal particles with a purity of greater than or equal to 99.99% are used as a metal source during each evaporation, metal sources used in every two adjacent evaporations are different, the thickness of the metal layer formed during the n-th evaporation is less than or equal to 20 nm, and the single-atom metal catalyst is obtained.The single-atom metal catalyst is prepared on the carbon film by adopting the vacuum thermal evaporation method more than twice, so that the single-atom metal catalyst can be prepared in a large area, and the single-atom metal catalyst has great potential for large-area and batch production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single-atom catalysis, in particular to a single-atom metal catalyst and a preparation method and application thereof. BACKGROUND

[0002] Catalysts play a crucial role in the fields of energy, information, and bioengineering. In order to improve the activity, selectivity, and atomic utilization of catalysts, single-atom catalysts that can provide single active sites have gradually become a hot spot in the field of catalysts and have attracted great attention in hydrogen evolution, oxygen reduction, and carbon dioxide reduction. Therefore, how to simply, universally, and low-costly prepare single-atom catalysts has become a promising development direction in the field of catalysis, and various preparation methods such as impregnation, coprecipitation, atomic layer deposition, and high-temperature atomic capture have emerged in an endless stream. For example, Cheng's group prepared a double-site Ru single-atom catalyst on S-doped carbon black by impregnation at room temperature, and this method was extended to Ir, Rh, Pt, and other elements. Zhang et al. prepared a Pt single-atom catalyst on iron oxide nanocrystals by coprecipitation of chloroplatinic acid and ferric nitrate. Stambula's group prepared a Pt single-atom catalyst on N-doped graphene nanosheets by atomic layer deposition, and the size of the Pt single-atom catalyst could be adjusted by controlling the number of atomic layer deposition cycles. Abhaya's group prepared a Pt single-atom catalyst on CeO2 support by heating Pt / La-Al2O3 and CeO2 powder at 800 DEG C for 10 hours, and found that the catalyst still existed after the CO oxidation reaction and was relatively stable.

[0003] However, the existing single-atom preparation methods still have their own limitations. For example, although the wet chemical method is low in cost, the reaction precision is difficult to control; although the atomic layer deposition method is high in precision, the reaction cost is high and the reaction conditions are high; and although the high-temperature atomic capture method is relatively simple, the reaction species are limited. Therefore, in the field of single-atom catalysis, it is necessary to provide a simple, low-cost, and universal method for preparing single-atom catalysts.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The present application provides a single-atom metal catalyst and a preparation method and application thereof, to solve the defects of the existing single-atom preparation methods, such as difficult control of reaction precision, high reaction cost, high reaction condition requirement, and limitation of reaction species. The single-atom metal catalyst is prepared on a carbon film by using a vacuum thermal evaporation method more than twice, which is simple in operation, low in cost, and requires only traditional materials, and can prepare a large-area single-atom metal catalyst, which has great potential for large-area and batch production of single-atom metal catalysts.

[0006] Specifically, the application provides a preparation method of a single-atom metal catalyst, comprising the following steps: evaporating a metal layer on a carbon film by a vacuum thermal evaporation method to obtain a substrate, and then evaporating n times on the substrate by the vacuum thermal evaporation method, wherein the layer structure obtained by the previous evaporation is used as the substrate for the next evaporation, the metal particles with a purity of greater than or equal to 99.99% are used as the metal source for each evaporation, the metal source used for each two adjacent evaporations is different, and the thickness of the metal layer formed in the n-th evaporation is less than or equal to 20 nm, so that the single-atom metal catalyst is obtained.

[0007] In the application, the layer structure obtained by the previous evaporation is used as the substrate for the next evaporation, that is, the layer structure obtained by the n-1th evaporation is used as the substrate for the n-th evaporation, and the layer structure obtained by the first evaporation is used as the substrate for the second evaporation, and the substrate for the first evaporation is the carbon film on which the metal layer is evaporated by the vacuum thermal evaporation method, wherein the metal layer is mainly arranged by metal particles when the metal layer is evaporated on the carbon film by the vacuum thermal evaporation method.

[0008] In the application, the evaporation is performed on the same side of the carbon film.

[0009] In the application, the single-atom metal catalyst refers to a substance in which a metal element exists in a single-atom structure and can play a catalytic role.

[0010] In the experiment, it is found that the carbon film and the thickness of the metal layer formed in the last evaporation play a key role in the process of preparing the single-atom metal catalyst, and if the carbon film is replaced by a dense metal film substrate, a glass or a silicon wafer which does not have a particle structure, or the thickness of the metal layer formed in the last evaporation is too large, the single-atom metal catalyst cannot be obtained. In order to obtain a higher content of single-atom metal, the thickness of the metal layer formed in the n-th evaporation is less than or equal to 10 nm.

[0011] According to the preparation method of the single-atom metal catalyst provided by the application, when n is greater than or equal to 2, the thickness of the metal layer formed by each evaporation on the substrate is less than or equal to 20 nm.

[0012] According to the preparation method of the single-atom metal catalyst provided by the application, the metal source used for evaporating the metal layer on the carbon film is Cu particles, Au particles or Ag particles.

[0013] According to the preparation method of the single-atom metal catalyst provided by the application, the thickness of the metal layer evaporated on the carbon film is generally within 20 nm.

[0014] The metal source used for the n times of evaporation on the substrate is Ag particles, Pd particles or Au particles.

[0015] The evaporation parameters for evaporating the metal layer on the carbon film are: the vacuum degree is 10 -3 Pa or below.

[0016] The evaporation parameters for evaporating the metal layer on the carbon film are: the vacuum degree is 10 -3 Pa or below.

[0017] The application further provides the single-atom metal catalyst prepared by the method for preparing the single-atom metal catalyst.

[0018] The single-atom metal catalyst provided by the application comprises a carbon film, metal particles on the carbon film and one or more single-atom metals on the metal particles.

[0019] The application further provides the application of the single-atom metal catalyst.

[0020] The single-atom metal catalyst and the preparation method and application thereof provided by the application have the advantages that, compared with various methods for preparing single-atom metal catalysts, the application first proposes a method for preparing single-atom metal catalysts on a carbon film by using more than two times of vacuum thermal evaporation, the method is simple and low in cost, and can be used to prepare large-area single-atom metal catalysts, has great potential for realizing large-area and batch production of single-atom metal catalysts, and in addition, the materials required by the method are traditional materials, can be widely applied to various metals, and can even be used to prepare catalysts loaded with single atoms of different elements, and has very important technical significance. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the application or prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without any creative effort.

[0022] Figure 1 is one of the schematic diagrams of the method for preparing the single-atom metal catalyst provided by the application;

[0023] Figure 2 is a schematic diagram of a preparation method of a monatomic metal catalyst provided by the present application;

[0024] Figure 3 is an atomic X-ray energy spectrum analysis diagram of a Cu20Ag10 monatomic metal catalyst in Example 1 provided by the present application; wherein, the bright green mark is Ag monatomic atoms existing on Cu nanoparticles;

[0025] Figure 4 is an atomic X-ray energy spectrum analysis diagram of a Cu20Pd10 monatomic metal catalyst in Example 2 provided by the present application; wherein, the bright yellow mark is Pd monatomic atoms existing on Cu nanoparticles;

[0026] Figure 5 is an atomic X-ray energy spectrum analysis diagram of a Cu4Pd1Au1 monatomic metal catalyst in Example 5 provided by the present application; wherein, the bright yellow mark is Pd monatomic atoms existing on Cu nanoparticles;

[0027] Figure 6 is an atomic X-ray energy spectrum analysis diagram of a Cu4Pd1Au1 monatomic metal catalyst in Example 5 provided by the present application; wherein, the bright green mark is Au monatomic atoms existing on Cu nanoparticles. DETAILED DESCRIPTION

[0028] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below in combination with the drawings in the present application. Obviously, the described embodiments are some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0029] The present application will be described below in combination with Figures 1-4 A monatomic metal catalyst, a preparation method and application thereof are described.

[0030] Unless specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in the art or according to the product instructions are used. Unless the manufacturers of the reagents or instruments are specified, the reagents or instruments are conventional products that can be purchased through a regular channel.

[0031] In the present application, the carbon film can be obtained by commercial purchase or self-preparation, as long as the carbon film is obtained by vacuum thermal evaporation of an amorphous carbon structure carbon rod on an organic substrate. The specific preparation process can be: first, coating the organic film layer on the substrate metal skeleton. Next, evaporate the amorphous carbon film on the substrate coated with the organic layer.

[0032] As Figure 1 shown, the preparation method of the single-atom metal catalyst of the present application mainly comprises the following steps:

[0033] Put the first high-purity metal particles and the carbon film into a high-vacuum resistance evaporation coating machine, and vacuumize to a vacuum degree of 10 -3 Pa or below, and adjust the current to uniform metal evaporation. After the metal layer of the first metal on the carbon film reaches the target value, quickly reduce the current and turn off the high-vacuum resistance evaporation coating machine. In the process of evaporating the metal layer onto the carbon film, the high-purity metal particles provide the metal source for the thermal evaporation, and the metal is evaporated onto the carbon film to form nucleation and grow. The vacuum degree in the quartz cover of the high-vacuum resistance evaporation coating machine will affect the purity of the product. Preferably, the vacuum degree in the quartz cover of the high-vacuum resistance evaporation coating machine is in the range of 10 -3 Pa or below, which can ensure the purity of the product and is easy to achieve in actual operation. The size of the current can also be adjusted to control the speed of the metal thermal evaporation, and then the thickness of the metal particles on the carbon film can be controlled by adjusting the thermal evaporation speed and the thermal evaporation time. The present application does not limit the thickness of the metal particles and the length and width of the carbon film, and the skilled person in the art can make appropriate adjustments according to the required size. After thermal evaporation, the porous morphology of the granular first metal on the carbon film provides a larger specific surface area and a larger number of active sites for the catalyst, which is beneficial to the improvement of the electrocatalytic activity of the material. Preferably, the particle size of the metal particles changes with the evaporation thickness. For the metal particles of the Cu20Ag10 co-evaporated catalyst with a thickness of 30 nm, the particle size is concentrated in the range of 5-10 nm.

[0034] Further, replace the metal source with the second high-purity metal particles, and place them together with the carbon film after thermal evaporation in the previous step into the high-vacuum resistance evaporation coating machine, and vacuumize to a vacuum degree of 10 -3 Pa or below, and adjust the current to uniform metal evaporation. After the metal layer of the second metal reaches the target value, quickly reduce the current and turn off the high-vacuum resistance evaporation coating machine. In the process of thermal evaporation, the second high-purity metal particles provide the metal source, and nucleate and grow on the carbon film after thermal evaporation in the previous step. After the second thermal evaporation, the second metal is thermally evaporated onto the surface of the first metal particles macroscopically, and the single atom of the second metal on the first metal particles can be observed microscopically, which is the single-atom metal catalyst. The type of metal can be appropriately adjusted according to the required type of catalyst.

[0035] In the present application, the i-th evaporated metal is denoted as M i , and the thickness of the evaporated M i is denoted as Y iThe monatomic metal catalyst prepared is named according to the type and thickness of the metal deposited layer by layer. For example, M1 with a thickness of Y1 is deposited on the carbon film, and then M2 with a thickness of Y2 is deposited, to obtain a catalyst of M1Y1M2Y2.

[0036] Further, as shown in the above steps, other types of metals can be continuously deposited on the material prepared to obtain a multi-layer monatomic metal catalyst. The present application does not limit the number of metal deposition layers, which can be appropriately adjusted according to the element composition and structure of the desired catalyst. In the last deposition, the thickness of the metal layer formed is ≤20 nm to ensure that the metal exists in the form of a single atom. Figure 2

[0037] Example 1

[0038] A method for preparing a monatomic metal catalyst, the steps of which are as follows:

[0039] (1) High-purity copper particles (purity ≥ 99.99%) are placed on a tungsten boat and fixed in a high-vacuum resistance evaporation film coating machine. A carbon film is fixed to the hot evaporation substrate. Vacuum is drawn to a vacuum degree of less than 10 -3 Pa, and the current is adjusted to uniform evaporation of the copper. After the thickness of the copper particles on the carbon film is detected to 20 nm by a film thickness detector, the current is quickly reduced, and the high-vacuum resistance evaporation film coating machine is turned off.

[0040] (2) The metal source is replaced with high-purity silver particles (purity ≥ 99.99%) placed on a tungsten boat and fixed in a high-vacuum resistance evaporation film coating machine. The carbon film after the copper is deposited in the above first step is fixed to the hot evaporation substrate. Vacuum is drawn to a vacuum degree of less than 10 -3 Pa, and the current is adjusted to uniform evaporation of the metal. After the thickness of the silver particles is detected to 10 nm by a film thickness detector, the current is quickly reduced, and the high-vacuum resistance evaporation film coating machine is turned off to obtain a monatomic metal catalyst Cu20Ag10.

[0041] The atomic X-ray energy spectrum analysis chart of the monatomic metal catalyst obtained in this example is shown in Figure 3 . The Cu20Ag10 monatomic metal catalyst obtained in this example retains the crystal structure of Cu, and there are some bright green marked Ag single atoms on the Cu nanoparticles.

[0042] Example 2

[0043] A method for preparing a monatomic metal catalyst, the steps of which are basically the same as those of Example 1, except that the high-purity silver particles used in step (2) are replaced with high-purity palladium particles (purity ≥ 99.99%) to prepare a monatomic metal catalyst Cu20Pd10. ​

[0044] The atomic X-ray energy spectrum analysis chart of the single-atom metal catalyst obtained in this embodiment is shown in Figure 2. The Cu20Pd10 single-atom metal catalyst obtained in this embodiment maintains the crystal structure of Cu, and there are some bright yellow marked Pd single atoms on the Cu nanoparticles. Figure 4 The atomic X-ray energy spectrum analysis chart of the single-atom metal catalyst obtained in this embodiment is shown in Figure 2. The Cu20Pd10 single-atom metal catalyst obtained in this embodiment maintains the crystal structure of Cu, and there are some bright yellow marked Pd single atoms on the Cu nanoparticles.

[0045] Example 3

[0046] A method for preparing a single-atom metal catalyst, the steps of which are basically the same as those of Example 1, except that the high-purity copper particles used in step (1) are replaced by high-purity gold particles (purity ≥ 99.99%), and a single-atom metal catalyst Au20Ag10 is prepared.

[0047] The Au20Ag10 single-atom metal catalyst obtained in this embodiment maintains the crystal structure of Au, and Ag single atoms are distributed on the Au nanoparticles.

[0048] Example 4

[0049] A method for preparing a single-atom metal catalyst, the steps of which are basically the same as those of Example 1, except that:

[0050] The high-purity copper particles used in step (1) are replaced by high-purity silver particles (purity ≥ 99.99%), and the high-purity silver particles used in step (2) are replaced by high-purity gold particles (purity ≥ 99.99%), and a single-atom metal catalyst Ag20Au10 is prepared.

[0051] The Ag20Au10 single-atom metal catalyst obtained in this embodiment maintains the crystal structure of Ag, and Au single atoms are distributed on the crystal structure of Ag.

[0052] From the tests of Examples 1-4, it can be seen that: the second metal will form single atoms on the aforementioned metal substrate without changing the crystal structure of the aforementioned metal by performing secondary evaporation on the carbon film evaporated with metal particles. The method of preparing a single-atom metal catalyst by secondary thermal evaporation is not affected by the type of metal within a certain thickness range, and is not limited to elements of the same group. Specifically: combining Examples 1 and 2, it can be obtained that the type of metal for secondary evaporation does not affect the formation of single atoms on the substrate evaporated with metal within a certain thickness range.

[0053] Combining Examples 1 and 3, it can be obtained that the type of metal for the first evaporation on the carbon film does not affect the formation of single atoms after secondary evaporation within a certain thickness range.

[0054] In combination with Embodiments 1, 2 and 3, it can be obtained that the two times of thermal evaporation of the metal is not limited to the same group of metals within a certain thickness range, and the second evaporation of different groups of metals can also form a single-atom metal catalyst.

[0055] In combination with Embodiments 3 and 4, it can be obtained that the order of the two times of thermal evaporation of the metal does not affect the formation of single atoms within a certain thickness range.

[0056] Therefore, the preparation method of the second thermal evaporation can simply and cheaply prepare a single-atom metal catalyst, and is not affected by the type of metal within a certain thickness range, and can universally prepare single-atom metal catalysts of different element compositions. In actual operation, the specific evaporation current reaction parameters and thermal evaporation time need to be determined in combination with the type of metal and the required thickness. Finally, the prepared single-atom metal catalyst can be used in the fields of carbon dioxide reduction, electrocatalytic hydrogen production, etc.

[0057] Embodiment 5

[0058] A preparation method of a single-atom metal catalyst, the steps of which are as follows:

[0059] (1) Place high-purity copper particles (purity ≥ 99.99%) on a tungsten boat and fix it in a high-vacuum resistance evaporation film coater. Fix the carbon film on the thermal evaporation substrate. Vacuumize to a vacuum degree less than 10 Pa, adjust the current to uniform evaporation of copper, and detect the thickness of the copper particles on the carbon film by a film thickness detector to 4 nm, then quickly reduce the current, and turn off the high-vacuum resistance evaporation film coater. -3

[0060] (2) Replace the metal source with high-purity palladium particles (purity ≥ 99.99%) placed on a tungsten boat and fix it in a high-vacuum resistance evaporation film coater. Fix the carbon film after evaporation of copper in the above first step on the thermal evaporation substrate. Vacuumize to a vacuum degree less than 10 Pa, adjust the current to uniform evaporation of the metal. Detect the thickness of the palladium particles by a film thickness detector to 1 nm, then quickly reduce the current, and turn off the high-vacuum resistance evaporation film coater. -3

[0061] (3) Replace the metal source with high-purity gold particles (purity ≥ 99.99%) placed on a tungsten boat and fix it in a high-vacuum resistance evaporation film coater. Fix the carbon film after evaporation of copper in the above first step on the thermal evaporation substrate. Vacuumize to a vacuum degree less than 10 Pa, adjust the current to uniform evaporation of the metal. Detect the thickness of the gold particles by a film thickness detector to 1 nm, then quickly reduce the current, and turn off the high-vacuum resistance evaporation film coater to obtain a single-atom metal catalyst Cu4Pd1Au1. -3

[0062] The atomic X-ray energy spectrum analysis diagram of the single-atom metal catalyst obtained in this embodiment is as follows:​​​Figure 5 and Figure 6 The Cu4Pd1Au1 monatomic metal catalyst obtained in the embodiment retains the crystal structure of Cu, and there are part of bright yellow marked Pd monatomic atoms and part of bright green marked Au monatomic atoms on the Cu nanoparticles.

[0063] The monatomic metal catalyst prepared above can be used for catalysis of water electrolysis to produce hydrogen, which is helpful for green and pollution-free production of hydrogen. In the experiment, the Faraday efficiency of hydrogen production of Cu20Ag5 at each potential is more than 70%.

[0064] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the present application.

Claims

1. A method for preparing a single-atom metal catalyst, characterized in that: include: After a metal layer is deposited on a carbon film by vacuum thermal evaporation to obtain a substrate, vacuum thermal evaporation is continued to be performed on the substrate twice, with the layer structure obtained by the first evaporation being used as the substrate for the second evaporation, and metal particles with a purity of ≥99.99% are used as a metal source in each evaporation, and the metal sources used in the two adjacent evaporation processes are different, thereby obtaining the single-atom metal catalyst; The thickness of the metal layer formed by the two evaporation processes on the substrate is ≤20 nm; The metal source used in evaporating the metal layer onto the carbon film is Cu particles; In the two evaporation depositions onto the substrate, the metal source used in the first evaporation is Pd particles, and the metal source used in the second evaporation is Au particles.

2. The method for preparing a single-atom metal catalyst according to claim 1, wherein: The thickness of the metal layer evaporated onto the carbon film is within 20 nm.

3. The method for preparing a single-atom metal catalyst according to claim 1 or 2, characterized in that: The evaporation parameters for evaporating the metal layer onto the carbon film are: vacuum degree 10 -3 Below Pa.

4. The method for preparing a single-atom metal catalyst according to claim 1 or 2, characterized in that: The evaporation parameters for the second evaporation on the substrate are: vacuum degree of 10 -3 Below Pa.

5. A single-atom metal catalyst prepared by the method for preparing a single-atom metal catalyst according to any one of claims 1 to 4.

6. Use of the single-atom metal catalyst according to claim 5, characterized in that: Used to catalyze the electrolysis of water to produce hydrogen or the reduction of carbon dioxide.

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