A method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films

Abstract

The present invention relates to the field of controllable preparation of nanomaterials, specifically a method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films. Metal nanoparticles are deposited on a nanocarbon film using physical deposition methods such as ion beam sputtering or magnetron sputtering. Rapid heating and cooling (at a heating and cooling rate of 100-300°C / s) in an inert atmosphere at a positive pressure (0.01-0.2 MPa above standard atmospheric pressure) and containing trace amounts of oxygen (oxygen volume fraction 0.001%-0.2%) causes the metal nanoparticles to form nanocrystals with a specific orientation, resulting in ultrafine (diameter <3 nm) metal nanocrystals (purity >95%) monodispersed on the nanocarbon composite film. By controlling the deposition conditions and the heating and cooling rates during rapid heating, the dispersion and size of the metal nanoparticles can be adjusted, resulting in metal nanocrystals with adjustable diameter and dispersion. Specifically, on a single-walled carbon nanotube film, the nanocrystals can be induced to form metal nanocrystals with a large aspect ratio by using tube bundle induction.

Description

Technical Field

[0001] The present invention relates to the field of controllable preparation of nano materials, in particular to a method for rapidly and controllably preparing an ultrafine metal nanocrystal / nanocarbon composite film. Background Art

[0002] Metal nanocrystals are nanometer-sized, with metal atoms arranged periodically to form specific crystal planes. Nanocrystals of varying structures possess exceptional optical, magnetic, mechanical, and electrical properties due to their unique orientation. The nanoscale dimensions of these exposed, specifically oriented crystal planes allow for selective adsorption of different molecules, resulting in promising applications in catalysis, sensing, and antibacterial applications.

[0003] In order to achieve controllable preparation of metal nanocrystals, researchers have invented two major methods: (1) "Top-down" physical methods, mainly including physical sputtering deposition, evaporation, ball milling, milling, etc. This type of method "breaks" the bulk metal material into tiny particles, and then forms metal nanocrystals during the heat treatment process. (Reference 1: Dhand, C.; Dwivedi, N.; Loh, XJ; Jie Ying, AN; Verma, NK; Beuerman, RW; Lakshminarayanan, R.; Ramakrishna, S. RSC Advances 2015, 5(127), 105003.; Reference 2: Gonzalez-Martinez, IG; Bachmatiuk, A.; Bezugly, V.; Kunstmann, J.; Gemming, T.; Liu, Z.; Cuniberti, G.; Rümmeli, MH Nanoscale 2016, 8(22), 11340.) This method can regulate the size and dispersibility of nanoparticles by changing the heat treatment process parameters. It has the advantages of strong controllability, good repeatability and high efficiency. However, the nanocrystals prepared by it generally have no regular morphology and poor structural uniformity. (2) "Bottom-up" chemical methods, mainly including electrochemical deposition, solvent thermal synthesis, coprecipitation, sol-gel, etc. This type of method uses heat or electricity as the driving force and surfactants as "templates" to make metal ions or atoms self-assemble to form metal nanocrystals. (Reference 3: Tsung, CK; Kuhn, JN; Huang, WY; Aliaga, C.; Hung, LI; Somorjai, GA; Yang, PD Journal of the American Chemical Society 2009, 131(16), 5816.; Reference 4: Xia, Y.; Gilroy, KD; Peng, H.-C.; Xia, X. Angewandte Chemie International Edition 2017, 56(1), 60.) This type of method can control the crystal plane, size and dispersibility of metal nanocrystals by changing the surfactant, reducing agent, heating temperature, and metal precursor salt concentration, and has strong adjustability and compatibility. However, this method is generally time-consuming, the size of the prepared nanocrystals is relatively large (>10nm), the structural uniformity of the nanocrystals is poor, the surface of the nanocrystals is coated with surfactants, and the nanocrystals in the solution need to be dispersed on a carrier for use.

[0004] In summary, metal nanocrystals have excellent physical and chemical properties and have broad application prospects in the fields of sensing and catalysis. However, their controllable preparation still faces many problems, such as: (1) The structural uniformity of metal nanocrystals is poor, and the surface is coated with surfactants. (2) The size of metal nanocrystals is large and difficult to control, and it is very difficult to prepare nanocrystals with a diameter of less than 3nm. (3) The preparation of nanocrystals is time-consuming and the synthesis efficiency is low. They still need to be dispersed on a carrier for subsequent use. Summary of the Invention

[0005] The present invention aims to provide a method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films. Monodisperse metal nanoparticles are deposited on a nanocarbon support via physical sputtering. Rapid temperature cycling reconstructs the nanoparticles into monodisperse, small-sized (<3nm), highly structurally uniform (>95%), and clean metal nanocrystals. Specifically, using a single-walled carbon nanotube film as a substrate, the carbon nanotube bundles can induce the metal nanocrystals to form ultrafine nanowires. The nanocarbon film-supported metal nanocrystal composite film exhibits high conductivity, a large specific surface area, and excellent mechanical properties, promising broad application prospects in fields such as electrochemistry.

[0006] The technical solution of the present invention:

[0007] A method for rapidly and controllably preparing an ultrafine metal nanocrystal / nanocarbon composite film comprises depositing metal nanoparticles on a nanocarbon film by ion beam sputtering or magnetron sputtering as a physical deposition method, and rapidly heating and cooling the metal nanoparticles in an inert atmosphere containing a positive pressure of 0.01 to 0.2 MPa higher than the standard atmospheric pressure and an oxygen volume fraction of 0.001% to 0.2% and a trace amount of oxygen at a heating and cooling rate of 100 to 300°C / s, so that the metal nanoparticles form high-purity, ultrafine nanocrystals with clean surfaces, thereby obtaining a composite film in which the metal nanocrystals are monodispersed in the nanocarbon film. By regulating the physical deposition conditions, metal nanoparticles with adjustable density and size are obtained, so that the size and dispersion of the nanocrystals are adjustable within a certain range.

[0008] The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite film, wherein the nanocarbon is carbon nanotube, graphene, graphyne, nanocarbon fiber, graphite or fullerene, and has good electrical conductivity, thermal conductivity and large specific surface area.

[0009] The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite film uses a carbon nanotube film composed of a highly crystalline carbon nanotube network with G / D>50, and the carbon nanotubes are single-walled, double-walled or few-walled carbon nanotubes.

[0010] The method for rapidly and controllably preparing an ultrafine metal nanocrystal / nanocarbon composite film uses single-walled carbon nanotube bundles to induce the growth of metal nanocrystals on a single-walled carbon nanotube film, forming ultrafine nanowires with a large aspect ratio, thereby obtaining a metal nanocrystal / nanocarbon composite film with a unique structure; wherein the aspect ratio of the ultrafine nanowires ranges from 1:1 to 5:1, and the diameter is less than 3nm.

[0011] The method for rapidly and controllably preparing an ultrafine metal nanocrystal / nanocarbon composite film enables the nanocarbon film carrying metal nanoparticles to achieve rapid heating and cooling, with both heating and cooling rates exceeding 100°C / s.

[0012] The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite film uses magnetron sputtering to deposit metal nanoparticles on the nanocarbon film. The sputtering power is 1 to 50 W, the deposition time is 10 to 500 seconds, the rapid heating temperature is 700 to 2200°C, and the heating and cooling rate is 100 to 300°C / s. Monodisperse metal nanocrystals with adjustable size within the range of 2 to 10 nm are prepared, and the purity of the nanocrystals is higher than 95%.

[0013] The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films improves the structural uniformity of the nanocrystals by performing one or more temperature ramping heat treatments in a positive pressure inert atmosphere. This method is time-efficient and highly controllable, and the inert atmosphere is high-purity Ar, He, or N2.

[0014] The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films controls the size and dispersion of nanoparticles by adjusting the physical deposition conditions of ion beam sputtering or magnetron sputtering, thereby achieving the preparation of monodisperse, size-adjustable ultrafine metal nanocrystals.

[0015] The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite film has poor wettability and chemical reaction activity with carbon, and the metal material is Au, Ag, Pt, Pd or Ir.

[0016] The method for rapidly and controllably preparing an ultrafine metal nanocrystal / nanocarbon composite film is disclosed. The Pt cubic nanocrystal / single-walled carbon nanotube composite film prepared by this method has excellent electrocatalytic performance. The fully exposed (100) crystal plane of the Pt cubic nanocrystal enables it to exhibit excellent oxygen reduction and ammonia oxidation performance in an alkaline environment.

[0017] The design idea of the present invention is:

[0018] The present invention supports metal nanoparticles on a nanocarbon film by physical deposition, and forms metal nanocrystals with a specific morphology through rapid heat treatment. The metal nanocrystals are directly dispersed on the nanocarbon film. The metal nanoparticles are supported on the nanocarbon film by a "top-down" method, and the nanoparticles are formed into nanocrystals with a regular morphology by rapid temperature increase and decrease, thereby obtaining a nanocarbon composite film supporting ultrafine metal nanocrystals.

[0019] Furthermore, by controlling the deposition conditions and the rapid heating ramp rate, the dispersion and size of the metal nanoparticles can be adjusted, resulting in metal nanocrystals with adjustable diameter and dispersion. Using single-walled carbon nanotube films as substrates, the tube bundles can induce the metal nanocrystals to form nanowires with a specific aspect ratio.

[0020] The advantages and beneficial effects of the present invention are:

[0021] 1. The present invention provides a method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films. After metal nanoparticles are loaded onto the nanocarbon film, the film is rapidly heated and cooled to form metal nanocrystals with regular morphology. The entire process can be completed within 1 minute, and the formed nanocrystals are small in size (<3nm), highly dispersed, and have a clean surface.

[0022] 2. This invention utilizes a top-down physical deposition method to control the composition, dispersion, and size of nanocrystals. Specifically, the size and dispersion of the prepared metal nanocrystals can be adjusted by varying the deposition conditions. Different types of metal nanocrystals can be obtained by using targets with different compositions. Using single-walled carbon nanotube films as a substrate, the tube bundles can induce the metal nanocrystals to form nanowires with a specific aspect ratio.

[0023] 3. The method of the present invention uses a nano-carbon film with a large specific surface area and high conductivity as a carrier. The prepared metal nanocrystals have a high structural consistency (>95%) and can be directly used as a self-supporting electrocatalytic thin film electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 . Transmission electron micrograph of Pt nanocrystal / single-walled carbon nanotube composite film after magnetron sputtering.

[0025] Figure 2 (a) Transmission electron micrograph of Pt cubic nanocrystal / single-walled carbon nanotube composite film and (b) size statistical histogram of Pt cubic nanocrystals; in (b), the abscissa "Particle size" is the particle size (nm), and the ordinate "Counts" is the number of counts.

[0026] Figure 3 .Composite film at 1mol·L -1Linear sweep voltammetry curve in KOH solution. In the figure, the square represents Pt cubic nanocrystal / single-walled carbon nanotube composite film, and the circle represents Pt nanocrystal / single-walled carbon nanotube composite film. The horizontal axis Potential represents the potential (V ver.RHE), and the vertical axis Current density represents the current density (mA cm -2 ). Scanning range 0.2V~1.0V.

[0027] Figure 4 .Transmission electron micrograph of high aspect ratio Pt ultrafine nanocrystal / single-walled carbon nanotube composite film.

[0028] Figure 5 . The composite film contains 0.1 mol·L -1 NH3 and 1 mol·L -1 Cyclic voltammetry curves in KOH mixed solution. In the figure, the square represents Pd cubic nanocrystal / nanocarbon fiber composite film, and the circle represents Pd nanocrystal / nanocarbon fiber composite film. The horizontal axis Potential represents the potential (V ver.RHE), and the vertical axis Current density represents the current density (mAcm -2 ). Scanning range: -1.0V~0V.

[0029] Figure 6 .Composite film at 1mol·L -1 Linear sweep voltammetry curve in KOH solution. In the figure, the square represents Pt cubic nanocrystal / graphene composite film, and the circle represents Pt nanocrystal / graphene composite film. The horizontal axis Potential represents the potential (V ver.RHE), and the vertical axis Current density represents the current density (mA cm -2 ). Scanning range: -1.4V~0V.

[0030] Figure 7 . Transmission electron micrograph of Pt nanoparticle / single-walled carbon nanotube composite film prepared by conventional temperature ramping.

[0031] Figure 8 .Transmission electron micrograph of Pt nanoparticle / SiN composite film. DETAILED DESCRIPTION

[0032] In practice, the present invention utilizes physical deposition methods such as magnetron sputtering or ion beam sputtering to deposit metal nanoparticles on a nanocarbon film. Magnetron / ion beam sputtering bombards different metal targets, regulating the sputtering power and deposition time to produce metal nanoparticles of varying sizes and densities. Under conditions of rapid heating and cooling (at a rate of 100-300°C / s) in an inert atmosphere at a positive pressure (0.01-0.2 MPa above standard atmospheric pressure) and containing trace amounts of oxygen (0.001%-0.2% by volume), the metal nanoparticles are transformed into nanocrystals with a specific morphology and orientation, yielding a metal nanocrystal / nanocarbon composite film. The composite film's structure is characterized, and its performance, including oxygen reduction and electrochemical ammonia oxidation, is tested.

[0033] Below, the present invention is further described in detail by examples.

[0034] Example 1

[0035] In this embodiment, the preparation of Pt cubic nanocrystal / single-walled carbon nanotube composite film, the specific experimental steps are:

[0036] (1) Deposition of metal nanoparticles

[0037] The single-walled carbon nanotube film was placed in a magnetron sputtering chamber and evacuated to a pressure of 1.0×10 -5 Pa, heated to 100 ° C, sputtered Pt, the ignition pressure was 20 Torr, the rotation speed was 10 rpm, the coating pressure was 5 Torr, the power was 10 W, the coating time was 500 s, and the film after sputtering deposited metal ( Figure 1 ) was placed in a rapid heating device, and the temperature was raised and lowered from 950°C within 20 seconds in an inert atmosphere of 99.9% He gas mixed with 0.1% O2 at a positive pressure of 0.13 MPa to obtain a Pt cubic nanocrystal / single-walled carbon nanotube composite film.

[0038] (2) Structural characterization of composite films

[0039] The Pt cubic nanocrystal / single-walled carbon nanotube composite film prepared in step (1) was placed in anhydrous ethanol and ultrasonicated for 10 minutes. Then, anhydrous ethanol containing Pt cubic nanocrystal / single-walled carbon nanotube was dripped onto the microgrid using a pipette. After drying, the film was observed under a transmission electron microscope. The morphology and size distribution of the film were as follows: Figure 2 As shown, the morphology of Pt cubic nanocrystals is rectangular or square, and the radial size of the short side is less than 3 nm.

[0040] (3) Performance test of composite films

[0041] The Pt cubic nanocrystal / single-walled carbon nanotube composite film prepared in step (1) was placed in an electrode holder as a working electrode, a carbon rod as a counter electrode, and a silver / silver chloride electrode as a reference electrode. -1 The linear sweep voltammetry curve (scan rate 5mV·s) was tested in a KOH mixed solution. -1 ), first introduce oxygen into the electrolyte for 10 minutes, and its oxygen reduction ability is as follows Figure 3 As shown, the half-wave potential of the Pt cubic nanocrystal / single-walled carbon nanotube composite film is increased by 153 mV compared with the Pt nanoparticle / single-walled carbon nanotube composite film.

[0042] Example 2

[0043] In this embodiment, the preparation of the Pt ultrafine nanowire / single-walled carbon nanotube composite film is carried out in the following specific experimental steps:

[0044] (1) Deposition of metal nanoparticles

[0045] Different from step (1) in Example 1, the film after sputtering and depositing the metal is placed in a rapid heating device, placed in an inert atmosphere with a positive pressure of 0.2 MPa and a volume fraction of 99.9% He gas mixed with 0.1% O2, and the temperature is raised and lowered by 1000°C five times within 30 seconds to obtain a Pt ultrafine nanowire / single-walled carbon nanotube composite film; wherein the aspect ratio of the ultrafine nanowires ranges from 1:1 to 5:1, and the diameter is less than 3 nm.

[0046] (2) Structural characterization of composite films

[0047] The Pt ultrafine nanowire / single-walled carbon nanotube composite film prepared in step (1) was placed in anhydrous ethanol and ultrasonicated for 10 minutes. Then, anhydrous ethanol with Pt cubic nanowires / single-walled carbon nanotubes was dripped onto the microgrid using a pipette. After drying, the film was observed under a transmission electron microscope. The morphology and size distribution of the film were as follows: Figure 4 As shown in the figure, the Pt cubic nanowires are all rectangular in shape, with the short side size less than 3 nm.

[0048] (3) Performance test of composite films

[0049] The same as step (3) in Example 1. The half-wave potential of the Pt ultrafine nanowire / single-walled carbon nanotube composite film is 10 mV higher than that of the Pt cubic nanocrystal / single-walled carbon nanotube composite film.

[0050] Example 3

[0051] In this embodiment, the preparation of Pd cubic nanocrystal / carbon nanofiber composite film, the specific experimental steps are:

[0052] (1) Deposition of metal nanoparticles

[0053] The nanocarbon fiber film was placed in an ion beam sputtering coating machine with the ion beam voltage set to 1250V, the ion beam current to 600mA, the acceleration voltage to 300V, the E / B ratio to 125%, the ion source argon flow rate to 18sccm, the neutralizer argon flow rate to 8sccm, the oxygen flow rate to 30sccm, and the substrate temperature to 200°C. After sputtering, the film was placed in a rapid heating device and heated and cooled from 1025°C within 20s under a positive pressure of 0.12MPa and an inert atmosphere of 99.999% Ar gas mixed with 0.001% O2 by volume to obtain a Pd nanocrystal / nanocarbon fiber composite film.

[0054] (2) Structural characterization of composite films.

[0055] The same as step (2) in Example 1, the obtained Pd cubic nanocrystals all have regular rectangular morphologies and the radial dimensions of the short sides are all 3 nm.

[0056] (3) Performance test of composite films

[0057] The Pd cubic nanocrystal / nanocarbon fiber composite film prepared in step (1) was placed in an electrode holder as a working electrode, a Pt electrode as a counter electrode, and a saturated calomel electrode as a reference electrode in a 0.2 mol·L -1 NH3 and 1 mol·L -1 Cyclic voltammetry was performed in a mixed solution of KOH (scan rate 5 mV·s -1 ), test the electrocatalytic oxidation activity of samples for ammonia in alkaline medium ( Figure 5 ), the anodic oxidation peak of Pd cubic nanocrystals / nanocarbon fiber composite film is 5.2 times higher than that of Pd nanoparticles / nanocarbon fiber composite film.

[0058] Example 4

[0059] In this embodiment, the preparation of Pt cubic nanocrystals / graphene composite films of different sizes is carried out in the following specific experimental steps:

[0060] (1) Deposition of metal nanoparticles

[0061] The Graphene film was placed in an ion beam sputtering device and vacuumed to a pressure of 3×10 -4 At 1.5 Pa, the current was set to 20 A and the voltage was 15 V to sputter Pt nanoparticles. The film after ion beam sputtering was placed in a rapid heating device. Under a positive pressure of 0.17 MPa and an inert atmosphere of 99.9% N2 mixed with 0.1% O2 by volume, the temperature was ramped from 1750°C within 20 seconds. This process was repeated 10 times to obtain a Pt cubic nanocrystal / graphene composite film.

[0062] (2) Structural characterization of composite films

[0063] The same as step (2) in Example 1, the obtained Pt cubic nanocrystals all have regular rectangular or square morphologies, and the radial dimensions of the short sides are all 3 nm.

[0064] (3) Performance test of composite films

[0065] The Pt cubic nanocrystal / graphene composite film prepared in step (1) was placed in an electrode holder, the electrode holder was used as the working electrode, the carbon rod was used as the counter electrode, and the silver / silver chloride electrode was used as the reference electrode. -1 The linear sweep voltammetry curve (scan rate 5mV·s) was tested in a KOH mixed solution. -1 ), to characterize the ability of the sample to release hydrogen in alkaline medium ( Figure 6 ), current density 200 mA cm -2 When the overpotential of Pt cubic nanocrystals / graphene composite film is -649 mV, it is smaller than the overpotential of Pt nanoparticles / graphene composite film -694 mV.

[0066] Comparative Example 1

[0067] The Pt nanoparticle / single-walled carbon nanotube composite film was prepared by conventional temperature ramping heat treatment. The specific experimental steps are as follows:

[0068] (1) Deposition of metal nanoparticles

[0069] Different from step (1) in Example 1, the film after sputtering is placed in an ordinary tube furnace in an inert atmosphere and heated and cooled at 1100°C within 1 hour to obtain a Pt nanoparticle / single-walled carbon nanotube composite film.

[0070] (2) Structural characterization of composite films

[0071] The same as step (2) in Example 1, transmission electron microscopy shows its structure as Figure 7 As shown in the figure, the size of the nanoparticles becomes significantly larger and has no regular morphology.

[0072] (3) Performance test of composite films

[0073] The same as step (3) in Example 1. The onset potential of the Pt nanoparticle / single-walled carbon nanotube composite film is significantly higher than that of the Pt cubic nanocrystal / single-walled carbon nanotube composite film, and the half-wave potential is increased several times.

[0074] Comparative Example 2

[0075] The Pt nanoparticle / SiN composite film was prepared using SiN as a carrier. The specific steps are as follows:

[0076] (1) Deposition of metal nanoparticles

[0077] Different from step (1) in Example 1, the substrate is a SiN film.

[0078] (2) Structural characterization of composite films

[0079] Same as step (2) in Example 1, the structure is as follows Figure 8 As shown in the figure, the size of the nanoparticles becomes significantly larger and has no regular morphology.

[0080] (3) Performance test of composite films

[0081] Similar to step (3) in Example 1, the initial potential of the Pt nanoparticle / SiN composite film becomes significantly higher, and the half-wave potential increases several times.

[0082] The results of the examples and comparative examples show that the metal nanocrystals prepared on the nanocarbon film by rapid temperature rise and fall have smaller size, higher density and higher structural uniformity. Compared with the prior art, the biggest feature of the present invention is that the metal nanoparticles supported on the nanocarbon network are rapidly heated and cooled (temperature rise and fall rate of 100-300℃ / s) under positive pressure (0.1-0.2MPa higher than standard atmospheric pressure) and in an inert atmosphere containing trace oxygen (oxygen volume fraction 0.001%-0.2%) to form metal nanocrystals with regular morphology, and the nanocarbon film-supported metal nanocrystal composite film is prepared quickly and controllably. The metal nanocrystals prepared by this method have high orientation consistency (purity>95%), clean surface, and are directly supported on the nanocarbon film with high specific surface area, high electrical conductivity and high thermal conductivity. They have broad application prospects in the fields of photothermal catalysis, energy storage and conversion, sensing and monitoring.

[0083] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to fall within the scope of the present invention.

Claims

1. A method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films, characterized in that: Metal nanoparticles were deposited on the nanocarbon film by physical deposition methods such as ion beam sputtering or magnetron sputtering. The metal nanoparticles were then rapidly heated and cooled in an inert atmosphere containing a positive pressure of 0.01-0.2 MPa above standard atmospheric pressure and an oxygen volume fraction of 0.001%-0.2% containing trace amounts of oxygen. The heating and cooling rates were 100-300 °C / s, allowing the metal nanoparticles to form high-purity, ultrafine, and surface-clean nanocrystals. Composite films in which the metal nanocrystals were monodispersed on the nanocarbon film were obtained. By regulating the physical deposition conditions, metal nanoparticles with adjustable density and size were obtained, and the size and dispersion of the nanocrystals were adjustable within a certain range. With a sputtering power of 1-50 W, a deposition time of 10-500 s, and a rapid heating temperature of 700-2200 °C, monodisperse metal nanocrystals with adjustable sizes in the range of 2-10 nm were prepared, and the purity of the nanocrystals was higher than 95%.

2. The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films according to claim 1, characterized in that: Nanocarbon is carbon nanotube, graphene, graphyne, nanocarbon fiber, graphite or fullerene, and has good electrical conductivity, thermal conductivity and large specific surface area.

3. The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films according to claim 2, characterized in that: The carbon nanotube film used is composed of a highly crystalline carbon nanotube network with a G / D ratio of greater than 50, and the carbon nanotubes are single-walled, double-walled or few-walled carbon nanotubes.

4. The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films according to claim 3, characterized in that: On a single-walled carbon nanotube film, single-walled carbon nanotube bundles are used to induce the growth of metal nanocrystals, forming ultrafine nanowires with a large aspect ratio, thereby obtaining a metal nanocrystal / nanocarbon composite film with a unique structure; among them, the aspect ratio of the ultrafine nanowires ranges from 1:1 to 5:1, and the diameter is less than 3 nm.

5. The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films according to claim 1, characterized in that: The nanocarbon film loaded with metal nanoparticles achieves rapid heating and cooling, with both heating and cooling rates greater than 100°C / s.

6. The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films according to claim 1, characterized in that: In a positive pressure inert atmosphere, the structural uniformity of the nanocrystals is improved by one or more temperature rise and fall heat treatments, which is time-consuming and well controllable. The inert atmosphere is high-purity Ar, He or N2.

7. The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films according to claim 1, characterized in that: By adjusting the physical deposition conditions of ion beam sputtering or magnetron sputtering to control the size and dispersion of nanoparticles, the preparation of monodisperse, size-adjustable ultrafine metal nanocrystals can be achieved.

8. The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films according to claim 1 or 3, characterized in that: The prepared metal nanocrystals have poor wettability and chemical reaction activity with carbon, and the metal material is Au, Ag, Pt, Pd or Ir.

9. The method for rapidly and controllably preparing ultrafine metal nanocrystal / nanocarbon composite films according to claim 1 or 3, characterized in that: The Pt cubic nanocrystal / single-walled carbon nanotube composite film prepared by this method has excellent electrocatalytic performance. The fully exposed (100) crystal plane of the Pt cubic nanocrystal enables it to exhibit excellent oxygen reduction and ammonia oxidation performance in an alkaline environment.

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