Method for synthesizing atomic dispersions

Abstract

Monoatomic and polyatomic dispersions, as well as systems and methods for synthesizing atomic dispersions, are disclosed. An exemplary method for synthesizing an atomic dispersion includes positioning a substrate loaded with at least one of an element precursor or an element cluster, applying one or more temperature pulses to the loaded substrate, the pulses applying a target temperature for a duration, maintaining a cooling period after the application of the pulses, and providing a monoatom of the element dispersed on the substrate after the one or more temperature pulses. The target temperature applied by the pulses is between 500 K and 4000 K, and the duration is between 1 millisecond and 1 minute.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of and priority to U.S. Provisional Patent Application No. 62 / 861,639, filed June 14, 2019, which is incorporated by reference herein in its entirety.

[0002] The present disclosure relates to the synthesis of atomic dispersions, and more particularly to the high temperature synthesis of mono- or poly-atomic dispersions. [Background technology]

[0003] Single-atom catalysts offer optimal atom utilization efficiency and unique coordination environments and are of great interest for improving catalytic performance for many reactions, such as biomass conversion, oxidation, hydrogenation, and electrocatalysis, among others. However, the stability of single-atom catalysts remains a challenge due to thermodynamically driven atomic aggregation and corresponding performance degradation.

[0004] To improve the thermal stability of single atoms, various approaches have been considered, such as by enhancing metal-substrate absorption using kinetic or spatial confinement, or by forming strong metal-substrate bonds. In general, atomic dispersion can be achieved by confining and coordinating the metal atoms to the substrate in wet chemical synthesis to prevent atomic agglomeration. Successful synthesis of single atom catalysts at higher temperatures gives higher thermal stability, but high temperature synthesis is difficult to achieve and incompatible with many temperature-sensitive methods and materials.

[0005] Furthermore, existing technologies are largely limited to single-element, single-atom catalysts, which do not realize the potential synergistic interactions between different atoms that can outperform single-atom catalysts and provide new functionality derived from multi-element interactions. Summary of the Invention [Problem to be solved by the invention]

[0006] The present disclosure relates to high temperature synthesis of mono- or polyatomic dispersions by heating pulses. Aspects of the present disclosure provide stable mono- and / or polyatomic groups dispersed on a substrate having stable atom-substrate bonds. [Means for solving the problem]

[0007] According to an aspect of the present disclosure, a method of synthesizing an atomic dispersion includes positioning a loaded substrate, the loaded substrate including a substrate loaded with at least one of an elemental precursor or an elemental cluster, and applying one or more temperature pulses to the loaded substrate, the one or more temperature pulses applying a target temperature for a duration, the target temperature being greater than or equal to 500 K and less than or equal to 4000 K, the duration being greater than or equal to 1 millisecond and less than or equal to 1 minute, maintaining a cooling period after application of the pulse, and providing a single atom of the element on the substrate after application of the one or more temperature pulses.

[0008] In various embodiments of the method, the method includes causing at least partial monoatomic dispersion of the element on the substrate during the pulse and forming atom-substrate bonds to stabilize the monoatoms of the element on the substrate.

[0009] In various embodiments of the method, each of the one or more temperature pulses applies a target temperature for a duration, and the method includes maintaining a cooling period after application of each of the one or more temperature pulses.

[0010] In various embodiments of the method, the method includes, during each of the at least one temperature pulse, causing at least partial monoatomic dispersion of the element on the substrate and forming atom-substrate bonds to stabilize the monoatoms of the element on the substrate.

[0011] In various embodiments of the method, the method includes performing iterative repetitions of at least one of loading a substrate with at least one of a precursor of the further element or a cluster of the further element, applying one or more further temperature pulses to the loaded substrate, each of the one or more further temperature pulses applying a target temperature for a duration, maintaining a cooling period after each application of the one or more further temperature pulses, and providing a polyatomic dispersion of the element and the further element on the substrate after application of the one or more further temperature pulses.

[0012] In various embodiments of the method, the element and the further element are one of the same element or different elements.

[0013] In various embodiments of the method, the element is one of Pt, Ru, or Co.

[0014] In various embodiments of the method, the substrate comprises one or more of a carbon-based material, a metal, a ceramic, a polymer, a composite material, or an oxide.

[0015] In various embodiments of the method, the substrate comprises one or more of carbon, C3N4, TiO2, or CO2-activated carbon nanofibers.

[0016] According to an aspect of the present disclosure, a system for synthesizing an atomic dispersion includes a substrate loaded with at least one of an elemental precursor or an elemental cluster, one or more heating elements, and a controller configured to control the one or more heating elements to apply one or more temperature pulses to the loaded substrate, the one or more temperature pulses applying a target temperature for a duration, the target temperature being between 500 K and 4000 K and having a duration between 1 ms and 1 min, and maintaining a cooling period after application of the pulse. After application of the one or more temperature pulses, single atoms of the element are dispersed on the substrate.

[0017] In various embodiments of the system, the pulse causes at least partial monoatomic dispersion of the element on the substrate and causes the formation of atom-substrate bonds to stabilize the monoatoms of the element on the substrate.

[0018] In various embodiments of the system, the one or more heating elements are configured to apply one of direct joule heating, conductive heating, radiative heating, microwave heating, laser heating, or plasma heating.

[0019] In various embodiments of the system, the controller is configured to control the one or more heating elements for each of the one or more temperature pulses to apply a target temperature for a duration and to maintain a cooling period after application of each of the one or more temperature pulses.

[0020] In various embodiments of the system, the system includes a conveyor for holding a loaded substrate, and the controller is configured to control the conveyor to transport the loaded substrate for heating by at least one heating element, and controlling the one or more heating elements to apply one or more temperature pulses to the loaded substrate includes controlling the one or more heating elements to maintain a temperature and controlling a speed of the conveyor to expose a portion of the loaded substrate to each of the one or more heating elements for a duration.

[0021] In various embodiments of the system, the one or more heating elements include multiple heating elements spaced apart such that transporting a portion of the loaded substrate on the conveyor between each of the multiple heating elements performs a cooling period.

[0022] In various embodiments of the system, the loaded substrate is a continuous strip and the conveyor continuously transports the continuous strip of the loaded substrate.

[0023] In various embodiments of the system, the loaded substrate is in one of a powder form or a droplet form, and the system includes an irradiating device for irradiating the loaded substrate through one or more heating elements, and controlling the at least one heating element to apply at least one temperature pulse to the loaded substrate includes controlling the at least one heating element to maintain a temperature and controlling an emission rate of the irradiating device to expose the loaded substrate to each of the at least one heating element for a duration.

[0024] In various embodiments of the system, the at least one heating element includes multiple heating elements spaced apart such that movement of the radiated load substrate between each of the multiple heating elements performs a cooling period.

[0025] In various embodiments of the system, the element is one of Pt, Ru, or Co.

[0026] In various embodiments of the system, the substrate comprises at least one of a carbon-based material, a metal, a ceramic, a polymer, a composite material, or an oxide.

[0027] In various embodiments of the system, the substrate comprises at least one of carbon, C3N4, TiO2, or CO2-activated carbon nanofibers.

[0028] According to an aspect of the present disclosure, a structure includes a substrate, a dispersed monoatom of an element on the substrate, and a bond between the monoatom and the substrate.

[0029] In various embodiments of the structures, the bond comprises one or more of a metallic bond, a covalent bond, an ionic bond, or Van der Waals forces.

[0030] In various embodiments of the structure, the element is one of Pt, Ru, or Co.

[0031] In various embodiments of the structure, the substrate comprises at least one of a carbon-based material, a metal, a ceramic, a polymer, a composite material, or an oxide.

[0032] In various embodiments of the structure, the substrate comprises at least one of carbon, C3N4, TiO2, or CO2-activated carbon nanofibers.

[0033] In various embodiments of the structure, the single atom is a catalyst for at least one of biomass conversion, oxidation, hydrogenation, thermochemical catalysis, electrochemical catalysis, photochemical catalysis, or fundamental research in atomic manipulation.

[0034] According to an embodiment of the present disclosure, the structure includes a substrate, polyatomic groups dispersed on the substrate, and bonds between the polyatomic groups and the substrate. Each of the polyatomic groups includes at least two atoms, where the at least two atoms are the same element or some of the at least two atoms are different elements. The polyatomic groups are selected from diatomic groups, triatomic groups, tetraatomic groups, or groups of more than four atoms.

[0035] In various embodiments of the structures, the bond comprises one or more of a metallic bond, a covalent bond, an ionic bond, or van der Waals forces.

[0036] In various embodiments of the structure, the polyatomic group includes two atoms of Pt-Ru.

[0037] In various embodiments of the structure, the polyatomic group includes two atoms of Pt-Co.

[0038] In various embodiments of the structure, the substrate comprises at least one of carbon nanofibers, reduced graphene oxide, or C3N4.

[0039] In various embodiments of the structure, the polyatomic group is a catalyst for at least one of biomass conversion, oxidation, hydrogenation, thermochemical catalysis, electrochemical catalysis, photochemical catalysis, or fundamental research in atomic manipulation.

[0040] Further details and aspects of the exemplary embodiments of the present disclosure are described in more detail below with reference to the accompanying drawings. [Brief description of the drawings]

[0041] The above and other aspects and features of the present disclosure will become more apparent from the following detailed description considered in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is a diagram of an exemplary control of a high temperature heating pulse according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram of an exemplary individual high temperature heating pulse according to an embodiment of the present disclosure. [Diagram 3] FIG. 3 is a diagram of an exemplary heating configuration for applying high temperature heating pulses according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a diagram of an exemplary process for synthesizing a monoatomic dispersion using high temperature heating pulses, according to an embodiment of the present disclosure. [Diagram 5] FIG. 5 is a diagram of an exemplary process for synthesizing polyatomic groups using high temperature heating pulses, according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a diagram of an exemplary result having three atomic groups, according to an embodiment of the present disclosure. [Figure 7] FIG. 7 is a diagram of an exemplary result with multiple atomic groups, according to an embodiment of the present disclosure. [Figure 8] FIG. 8 is a diagram of an exemplary heating configuration having multiple heating elements and a conveyor, according to an embodiment of the present disclosure. [Figure 9] FIG. 9 shows graphs and images relating to the application of a high temperature heating pulse (HTHP) process to synthesize Pt atoms on a CO2-activated carbon nanofiber (CA-CNF) substrate according to an embodiment of the present disclosure. [Figure 10] FIG. 10 shows diagrams and graphs relating to single atom bonding structures according to embodiments of the present disclosure. [Figure 11]FIG. 11 shows graphs and images relating to the application of the HTHP process to various atoms and substrates, and for various applications, according to an embodiment of the present disclosure. [Figure 12] FIG. 12 shows diagrams and images of the formation of Pt-Ru diatomic atoms on carbon nanofibers by the HTHP process according to an embodiment of the present disclosure. [Figure 13] FIG. 13 shows high-resolution atomic images of the formation of two atoms on carbon and C3N4 substrates by HTHP process, according to an embodiment of the present disclosure. [Figure 14] FIG. 14 is a diagram of an exemplary heating configuration for applying a HTHP process to micronized powder or droplet substrate particles, according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] The present disclosure relates to high temperature synthesis of monoatomic or polyatomic dispersions by heating pulses. Aspects of the present disclosure provide stable monoatomic and / or polyatomic groups dispersed on a substrate having stable atom-substrate bonds. Temperatures represented by the letter "K" are understood to refer to Kelvins and temperatures represented by the letter "C" are understood to refer to Celsius.

[0043] The synthesis process disclosed herein may be referred to as a process of high temperature heating pulses ("HTHP"). The HTHP process synthesizes and stabilizes single atoms at high temperatures and can be achieved using programmable periodic on-off heating pulses with short on-states (e.g., for <55 ms, ~1500 K) and long off-states (e.g., 10 times longer than the on-state, near room temperature). In various embodiments, the on-state provides the activation energy for single atom dispersion by forming atom-substrate bonds that can naturally sustain high temperature annealing. The longer off-state achieves overall dispersion stability by preventing extended heating induced atom agglomeration, metal evaporation, and substrate degradation. The on-off heating pulses provide atom dispersion while keeping the substrate stable during high temperature exposure.

[0044] As described later in this specification, the HTHP process can be applied to synthesize polyatomic groups or atomic alloys composed of the same or different elements, each element being monoatomic and bonded to each other and to the substrate. As used herein, the term "polyatomic group" refers to and includes groups of two or more atoms on a substrate resulting from the sequential application of the HTHP process, such as groups of two atoms, three atoms, four atoms, or other numbers of atoms. The atoms of a polyatomic group may be the same element or different elements. For example, all atoms in a polyatomic group may be the same element, or all atoms in a polyatomic group may be different elements, or some atoms in a polyatomic group may be different elements, while some atoms in a group are the same element. Examples of polyatomic groupings are described later in this specification in connection with Figures 5-7.

[0045] Portions of this disclosure refer to U.S. Provisional Patent Application No. 62 / 861,639, filed June 14, 2019, which is incorporated by reference in its entirety and may be referred to herein as the “supplement.”

[0046] Referring now to FIG. 1, a diagram of an exemplary control of a high temperature heating pulse is shown. The diagram of FIG. 1 is not intended to be drawn to scale. The heating pulse is high In various embodiments, various pulses can be controlled to achieve a heat on state target temperature of T high Unable to achieve T high During the heating off state, T low The process can be controlled to achieve an off-state target temperature of 1000° C. In various embodiments, the various off-states can be controlled to achieve a precise temperature T low Unable to achieve T low The temperature T can have a temperature above or below T and different off-state periods can achieve different temperatures. low may be, for example, at room or ambient temperature.

[0047] A heating configuration for implementing the temperature pulse control of FIG. 1 is described below in conjunction with FIG. 3. Currently, the temperature T high and T low It is sufficient to note that temperature T may be sensed by one or more temperature sensors that may sense the temperature of the heating element or may sense the temperature of the surroundings close to the material being heated. In various embodiments, the temperature T high and T low may be estimated based on predetermined heating characteristics of the heating element and the heating environment, such as when a temperature sensor is not used at all or not used in a desired location.

[0048] The control diagram of FIG. 1 is exemplary, and variations are considered within the scope of the present disclosure. For example, although a number of n pulses is shown, the HTHP process can be performed with only a single pulse (n=1) in various scenarios. In addition, the pulse control is programmable and different control patterns can be implemented. For example, in various embodiments, various pulses can have different target temperatures. Such variations are intended to be within the scope of the present disclosure.

[0049] FIG. 2 is a diagram of an exemplary individual high temperature heating pulse. The diagram in FIG. 2 is not intended to be drawn to scale. The heating pulses may or may not be constant, e.g., 10 K / min and 10 7 The heating rate R may be between (inclusive) K / min heating The target temperature T high When is achieved, the temperature may be controlled at the target temperature for the duration of various embodiments, and the target temperature T high can be 500 K or more and 4000 K or less, and the duration t high can be greater than or equal to 1 ms and less than or equal to 1 min. For example, a target temperature T between 1500 K and 2000 K high If , the duration t to maintain the target temperature highcan be approximately 55 milliseconds. As mentioned above, the actual temperature achieved is precisely T high Instead, it may be higher or lower than the target temperature.

[0050] Temperature lasts for t high After being controlled at the target temperature for a period of cooling The temperature may or may not be constant, and may be controlled to decrease at, for example, −10 K / min and −10 7 The target temperature T low When this is achieved, the temperature low In various embodiments, the target temperature T low can be room temperature or ambient temperature, and the duration T to maintain the target temperature low is the duration t high The duration T low is the majority of the duration t high It is not necessary that the duration be 10 times that of the time t , but may be another duration. For example, a duration of t ≈ 55 ms may be used. high For duration t low can be about 550 ms. As mentioned above, the actual temperature achieved is precisely T low Instead, it may be higher or lower than the target temperature.

[0051] The illustration of FIG. 2 is exemplary and variations are intended to be within the scope of the present disclosure. For example, heating and cooling rate R cooling Although shown as a constant rate, it may be a variable rate controlled according to a programmed progression. In addition, the heating rate R heating and cooling rate R coolingmay vary significantly from one another, such as when the cooling rate is achieved passively. In various embodiments, the cooling rate can be achieved by active cooling. Such and other variations are intended to be within the scope of the present disclosure.

[0052] Referring now to FIG. 3, a diagram of an exemplary heating configuration for applying a high temperature heating pulse is shown. According to aspects of the present disclosure, any heating configuration can be used, provided that the temperature pulse can be controlled in the manner described in connection with FIG. 1 and FIG. 2. For example, FIG. 3 shows six possible configurations, including direct Joule heating, conductive heating, radiative heating, microwave heating, laser heating, and plasma heating. However, other heating configurations not shown or described herein can also be used. The various configurations can be implemented with cooling mechanisms (not shown), such as, but not limited to, cooling by radiation and conduction, active cooling by conduction and convection, and / or active cooling by physical or chemical transitions that absorb heat, among other possibilities. Depending on which heating configuration is implemented, one or more temperature sensors (not shown) can be placed in one or more locations, as described above. In various embodiments, the temperature can be estimated based on the predetermined heating characteristics of the heating element and the heating environment, such as when no temperature sensor is used at all or not used at the desired location.

[0053] The heating arrangement may include a controller (not shown) implemented or programmed to control the heating pulses in the manner described in connection with Figures 1 and 2. The controller may include, for example, one or more of a central processing unit, a microcontroller, a digital signal processor, a field programmable gate array (FPGA), a programmable logic device (PLD), and / or an application specific integrated circuit (ASIC), among other types of processors and circuits. The heating arrangement may also include other components, such as, but not limited to, a power source, a fuel source, a motor, a housing, insulation, and / or other sensors. Such components are not shown to provide a clearer view, but will be understood and appreciated by those skilled in the art.

[0054] FIG. 4 is a diagram of an exemplary process for synthesizing monoatomic dispersions using high temperature heating pulses. Precursors or atomic clusters of elements 410 are loaded onto a substrate 420, and the loaded substrate is subjected to a HTHP process. The loaded substrate 410 / 420 can be treated, for example, with the heating configuration shown in FIG. 3. The HTHP process converts the precursors 410 into the desired atoms 430 and / or disperses the atomic clusters 410. The high temperature on-state of the HTHP process promotes monoatomic 430 dispersion and stabilization through strong atom-substrate bonding, while the off-state achieves overall stability by preventing overheating induced atomic agglomeration and substrate degradation. The on-off heating pulses result in atomic dispersions 430 on the substrate 420 while keeping the substrate 420 stable during the high temperature exposure. The monoatomic dispersion achieved by the HTHP process does not disperse all clusters, and some clusters may remain after the HTHP process.

[0055] In various embodiments, the monatoms 430 can be any monatoms including, but not limited to, Pt, Ru, or Co. In various embodiments, the substrate 420 can be a carbon-based, carbon-based material, a metal, a ceramic, a polymer, a composite, an oxide, and / or a combination thereof. For example, the substrate 420 can be a carbon, C3N4, or TiO2 substrate, or a CO2-activated carbon nanofiber (CA-CNF) substrate. As used herein, the term "defect" refers to a feature of the substrate and refers to and includes irregularities in the substrate structure and / or deviations / deviations from the substrate's regular structure. As discussed above, defects in the substrate act to stabilize the monatoms on the substrate. The illustration of FIG. 4 is exemplary and is not intended to be drawn to scale. For example, the monatoms 430 may not be evenly or regularly spaced on the substrate 420. In various embodiments, the monatoms 430 can have non-uniform or irregular spacing. Furthermore, not all atoms of an element on the substrate 420 are single atoms, but rather portions of the substrate 420 may include groups of multiple atoms of an element.

[0056] 5 is a diagram of an exemplary process for synthesizing polyatomic groups using high temperature heating pulses. A precursor or cluster of element A 510 is loaded onto a substrate 520 and a HTHP process is applied to the loaded substrate to provide monoatomic dispersion and stabilization 530. A precursor or cluster of element B 540 is then further loaded onto the substrate 520 and a HTHP process is applied to the further loaded substrate to provide monoatomic dispersion and stabilization of atom B 542. By this process, atom B 542 can be dispersed and stabilized on the substrate 520 at the same location as atom A 512, thereby forming a polyatomic group, and / or dispersed and stabilized on the substrate 520 at a different location than atom A 512. In various embodiments, atom A and atom B can be the same element, or atom A and atom B can be different elements.

[0057] The diagram of FIG. 5 is illustrative and is not intended to be drawn to scale. For example, the monoatoms and polyatomic groups may not be evenly or regularly spaced on the substrate. In various embodiments, the monoatoms or polyatomic groups may have non-uniform or irregular spacing. In various embodiments, not all atoms A 512 are grouped with atoms B 542, and not all atoms B 542 are grouped with atoms A 512. Furthermore, a particular group on the substrate 520 may include multiple atoms A 512 or multiple groups of atoms B 542. In other words, the monoatomic dispersion achieved by the HTHP process does not disperse all clusters, and some clusters may remain after the HTHP process. In various embodiments, the monoatoms 512, 542 may be any monoatom, including, but not limited to, Pt, Ru, and / or Co. In various embodiments, the substrate 520 may be a carbon-based material, a metal, a ceramic, a polymer, a composite, an oxide, and / or a combination thereof. For example, the substrate 520 can be a carbon, C3N4, or TiO2 substrate, or a C02 activated carbon nanofiber (CA-CNF) substrate.

[0058] The process of further loading the substrate with another precursor or cluster of the element can be repeated to form larger groups of multiple atoms. For example, FIG. 6 is an illustration of an exemplary result having a triatomic group formed by atom A 610, atom B 620, and atom C 630 on a substrate 640, and FIG. 7 is an illustration of an exemplary result having a polyatomic group of n atoms formed by atom A 710, atom B 720, atom n 730 on a substrate 740. The results of FIGS. 6 and 7 can be achieved by continuously / repeatedly loading substrates and applying the HTHP process to the loaded substrates. The atoms of each group can be the same element or can include different elements. In various embodiments, the monoatoms can include any monoatom, for example, but not limited to, Pt, Ru, or Co. The substrate can be a carbon-based material, a metal, a ceramic, a polymer, a composite, an oxide, and / or a combination thereof. For example, the substrate can be a carbon, C3N4, or TiO2 substrate, or a CO2-activated carbon nanofiber (CA-CNF) substrate.

[0059] The resulting substrates having monoatomic and / or polyatomic dispersions can be used in a variety of applications, including, but not limited to, biomass conversion, oxidation, hydrogenation, thermochemical catalysis, electrochemical catalysis, photochemical catalysis, and / or fundamental research in atomic manipulation, among others.

[0060] Thus, what has been described above are examples of systems and methods for implementing high temperature heating pulses. Below, examples of specific systems or examples of specific materials and substrates that are treated with high temperature heating pulses are described.

[0061] 8 shows a diagram of an exemplary heating configuration having multiple heating sources / elements 810 and a conveyor 820 that carries one or more loaded substrates 830 to be heated by the heating elements 810. The heating elements 810 may remain heated and their temperature may not need to be increased or decreased. Rather, the speed of the conveyor 820 is increased or decreased for a duration t highThe positions of the heating elements 810 can be configured to expose the loaded substrate 830 to the individual heating elements 810 for a duration t low When the illustrated configuration is used with a continuous strip of substrate 830 loaded with elemental precursors or clusters, the HTHP process can be applied continuously to synthesize mono- or polyatomic dispersions 840 at high synthesis rates.

[0062] Referring to FIG. 14, a diagram of an exemplary heating configuration for applying a HTHP process to finely divided powder or droplet substrate particles according to an aspect of the present disclosure is shown. The illustrated heating configuration includes a number of heating elements 1410 that can emit finely divided powder or droplet substrate particles 1420 (e.g., aerosolized) by an emitter device (not shown), such as a sprayer or blower. In various embodiments, the finely divided powder or droplet substrate particles 1420 can have a substrate comprising a carbon-based material, a metal, a ceramic, a polymer, a composite material, an oxide, and / or a combination thereof. The finely divided powder or droplet substrate particles 1420 can be loaded with elemental precursors or elemental clusters. The heating elements 1410 can remain heated and their temperature does not need to be increased or decreased. Rather, the speed at which the finely divided powder or droplet particles 1420 are emitted is determined by the duration t corresponding to the on state of FIG. 2. high The positions of the heating elements 1410 can be configured to expose the loaded powder or droplet substrate particles 1420 to the individual heating elements 1410 for a duration t low When the illustrated configuration is used with a continuous flow of finely divided powder or droplet substrate particles loaded with precursors or clusters of elements 1420, the HTHP process can be continuously applied to synthesize mono- or polyatomic dispersions on the finely divided substrate particles 1430 at high synthesis rates.

[0063] The application of the HTHP process to specific atoms and substrates is described below. In the following description, any of the heating configurations may be used, such as any of the heating configurations of FIG. 3, FIG. 8, or FIG.

[0064] Figure 9 shows graphs and images for applying the HTHP process to synthesize Pt atoms on CO2-activated carbon nanofiber (CA-CNF) substrate. In Figure 9, part (a) is a schematic diagram showing the HTHP synthesis and dispersion process, including carbon atoms, metal precursors and metal atoms. Part (b) shows the temperature evolution and detailed heating / cooling patterns during HTHP synthesis. The inset shows the light emitted from the material at high temperature. Part (c) shows the 10-pulse heating pattern, showing the uniform temperature in each cycle with high temperature on and low temperature off states. Parts (d) and (e) show the results of the HTHP method (0.01 μmol / cm 2 Part (f) shows high angle annular dark field (HAADF) images of a Pt single atom after 1 and 10 cycles of HTHP process. Part (f) shows extended X-ray absorption fine structure (EXAFS) profiles (without phase correction) for a Pt single atom on CA-CNF after 1 and 10 cycles of HTHP process.

[0065] As shown diagrammatically in part (a) of FIG. 9, an ethanol-based salt precursor (HPtCl) was added to defective CA-CNF (e.g., 0.01 μmol / cm 2The precursor-loaded CA-CNF membrane is then subjected to the HTHP process using an electric Joule heating process that can be programmed in terms of temperature, on-off duration, and repeated cycles (Supplementary, Figure SI). Thermal images captured with a high-speed camera show a uniform spatial temperature distribution during the shock heating process (Supplementary, Figure S2). Part (b) of Figure 9 shows the temperature evolution of a pulse that is heated to -1500 K for 55 ms and then rapidly quenched by directly cutting off the input current for 10 times longer, resulting in an average temperature of ~400 K for the entire process. Part (c) of Figure 9 shows the temperature profile with 10 heating cycles over 6 s, illustrating the relatively stable temperatures that can be repeatedly achieved during the heating process. Furthermore, temperatures up to ~3000 K can be achieved (Supplementary, Figure S2c), allowing the synthesis of thermally stable single-atom nanotubes at high temperatures.

[0066] Parts (d) and (e) of Figure 9 show high-angle annular dark-field (HAADF) images of Pt dispersed on the CA-CNF substrate after 1 and 10 heat pulses at 1500 K. After a single heat pulse, the surface of the CA-CNF was dispersed with a high density of monoatoms, but Pt clusters were also visible (part (d) of Figure 9, and Supplementary Fig. S3a). However, after 10 pulses, the substrate showed a relatively uniform monoatomic distribution (part (d) of Figure 9, and Supplementary Fig. S3b), indicating further decomposition of the clusters into monoatoms during the successive HTHP processes. The monoatomic dispersion is confirmed by macroscopic extended X-ray absorption fine structure (EXAFS) (Figure 9, part (f)) and X-ray near-edge structure (XANES) analysis (Supplementary Fig. S3c). The EXAFS spectrum of the 1-cycle sample shows a weak peak at ~2.5 Å corresponding to Pt-Pt bonds, and a dominant peak at ~1.5 Å indicative of Pt-substrate bonds (as discussed below, Pt-C bonds), revealing a structure of Pt nanoclusters mixed with monoatoms. After 10 cycles, almost no P-Pt bonds remain, indicating the dominance of monoatomic dispersion by breaking down the remaining clusters. The CA-CNF substrate is ~56 m 2 / g surface area, and the Pt loading is measured to be ~0.24 wt%. By varying the metal loading, nanoclusters can be formed at higher loadings (Supplementary, 0.05 and 0.1 μmol / cm) due to limited stabilization sites. 2 (see Fig. S4 for the case).

[0067] To characterize the dispersion mechanism, comparative control samples using different heating strategies (Supplementary, Figure S5a-c) are examined. Low-temperature synthesis may lack the activation energy (i.e., poor dispersion and stability) to effectively disperse and bond these atoms to the substrate, while high-temperature annealing may result in overheating-induced graphitization of the carbon substrate (i.e., loss of defects) and unacceptable particle agglomeration due to long-range atomic diffusion. Although the HTHP process utilizes high temperatures for monoatomic synthesis, each pulse is short enough to avoid substrate degradation, thereby maintaining the stability of the monoatomic dispersion.

[0068] As mentioned above, substrate defects help to bind mobile monatoms onto the substrate and improve its structural stability (see Supplementary, Fig. S5d-f). When the HTHP process is applied to relatively crystalline CNFs (without CO2 activation), nanoclusters mixed with monatoms are obtained due to the limited defect sites. In contrast, after activation, the improved defect concentration and the presence of micropores (i.e., carbon vacancies) on CA-CNFs (Supplementary, Fig. S6-S7) result in high density monatomic dispersion. Thus, a more defective substrate can accommodate a high density of monatoms. Thus, this illustrates the role of high temperature heating pulses and defects on the substrate for effective monatomic dispersion and stabilization.

[0069] The Pt monoatoms synthesized by the HTHP process have structural stability, especially when synthesized at a high temperature of 1500 K, which can be confirmed by in situ scanning transmission electron microscopy (STEM) from room temperature to 1273 K. The samples are allowed to stabilize for at least 30 min before taking images. As shown in Supplementary Fig. 2a, the Pt monoatoms show uniform and dense monoatomic dispersion at each temperature up to 1273 K after holding for 60 min. Furthermore, the stability of the Pt monoatoms can be confirmed by ex situ thermal annealing at 1073 K for 1 h in a furnace with Ar flow (Supplementary Fig. S8). Since the HTHP process can utilize temperatures through 3000 K (Supplementary Fig. S2c), the HTHP process can enable the synthesis of monoatoms at even higher temperatures. For example, the HTHP method can be applied to synthesize monoatoms at 1800 K and 2000 K (0.005 μmol / cm). 2 With a smaller loading of , a stable monoatomic dispersion can be seen by both STEM and EXAFS measurements (Supplementary, Fig. 2c and Fig. S9).

[0070] For comparison, Supplementary Fig. 2d shows reports of monoatoms synthesized using various methods. Most wet chemical approaches use mild temperatures, and the resulting monoatoms are fragile under subsequent high-temperature annealing, especially in the absence of proper bonding or coordination with the substrate. Furnace heating or annealing at 1073-1173 K can substantially increase the thermal stability of the monoatoms by creating strong and stable metal-substrate bonds through atom trapping and substrate anchoring. However, the much higher temperature of the HTHP process surpasses furnace heating in its ability to synthesize monoatoms through 1500-2000 K. Furthermore, high-temperature synthesis offers ultrafast kinetics for monoatom dispersion with much shorter processing times (e.g., <10 s) and higher efficiency compared to low-temperature methods.

[0071] For the single-atom bond structures, the thermal stability resulting from the HTHP process comes from the ability of the Pt-substrate bond to resist high-temperature annealing. Figure 10 shows diagrams and graphs for the single-atom bond structures. Part (a) shows the first shell model EXAFS fit of the Fourier transform at the Pt L3 edge for the Pt-1500K-10 cycle sample, indicating a bond length of 1.931 Å with a coordination number of 2.8. Part (b) shows density functional theory (DFT) calculations of bond lengths in the Pt-C3, Pt-N3, and Pt-O2C2 configurations. Part (c) shows molecular dynamics (MD) simulations for the single-atom dispersions (I-III) and subsequent annealing at 1500 K (IV). Part (d) shows the Pt-Pt (type 1) and Pt-C bonds (types 2-10) identified in the dispersion system. Part (e) shows the statistical distribution of bond configurations before and after shock wave synthesis (III), where weak bonds become strong Pt-C bonds. (f) shows the energetic analysis of Pt atoms deviated from a Pt-30 cluster by forming a thermodynamically stable Pt-C bond (type 10). Part (g) shows the time required for monoatomic dispersion, and part (h) shows the associated bond configurations at different synthesis temperatures. High temperature provides the activation energy for bond formation, indicating higher dispersion efficiency with more stable Pt-C bonds (types 5-10) at higher synthesis temperatures.

[0072] Continuing to refer to Figure 10, the bond structure can be analyzed by extracting the nearest-neighbor coordination number and local structure of the Pt single atom from the fitting of the EXAFS profile with the first-shell model (Supplementary, Table 1 and Figure S10). Part (a) of Figure 10 shows the EXAFS fitting of the Pt 1500 K single atom, providing a bond spacing of 1.931 Å and a coordination number of 2.8 (indicating a Pt-X3 bond configuration). The bond length is significantly shorter than the literature reports of Pt-0 (2.01-2.05 Å) and Pt-N bonds (~2.3 Å), but in good agreement with the calculated bond length of 1.93 Å for the Pt-C bond. Furthermore, based on this PCX3 bond model, density functional theory (DFT) can be used to calculate the bond distances of Pt-C in Pt-Ci, Pt-N in PCN3, and Pt-0 in Pt-02C2. The calculated Pt-C bond in the Pt-C3 configuration shows a bond distance of 1.940 Å, which is very close to the fitted result, while the Pt-N and Pt-0 bonds all have much larger bond distances (Figure 10, part (b)), confirming the Pt-C bond structure in the sample.

[0073] DFT results also show that the binding energy of Pt-C bonds is higher than that of Pt-N bonds under similar bond configurations (Pt-X3 and Pt-X4) (Supplementary Fig. 11a). Moreover, the charge density difference diagram further shows the difference between Pt-C and Pt-N bonds, where a large amount of charge transfer appears between Pt and C atoms in Pt-C bonds and the charge density is mainly concentrated at the center, indicating a strong covalent bond nature. Meanwhile, in Pt-N bonds, the transferred electrons mainly circulate around Pt and N atoms, indicating an ionic bond (Supplementary Fig. S11b). Thus, Pt-C bonds show a higher binding energy and unique covalent bond nature compared to Pt-N bonds in similar bond configurations.

[0074] To understand the atomic origin of the high-temperature-induced dispersion and stabilization, molecular dynamics (MD) simulations using a reaction force field (ReaxFF) potential can be performed (see Supplementary, S1 Methods section). The defects on the graphene include randomly etched carbon vacancies, similar to the surface of CA-CNF. Part (c) of Figure 10 shows the dispersion of Pt clusters into single atoms upon increasing heating cycles at 1500 K (I–III), as well as the dispersion stability upon thermal annealing at 1500 K (IV). Both aggregation and granulation of Pt atoms are seen, but the granulation can only be stabilized if energetically favorable Pt-C bonds are formed (types 4–10, part (d) of Figure 10). Part (e) of Figure 10 shows the evolution of the bond structure before and after the HTHP process at 1500 K, and all the initial weak bonds (Pt-Pt and type 1-3 Pt-C) change into strong Pt-C bonds (type 4-10) with higher bond energy, indicating the atomic origin of why the monatoms synthesized by the HTHP process are more thermally stable than the Pt clusters. The simulation clearly reproduced the synthesis process in which the initial Pt clusters were weakly attached to the substrate, but with more HTHP heating, the clusters were broken down into monatoms by forming strong Pt-C bonds that could sustain high-temperature annealing. This also indicates that the defects act to stabilize the monatoms and determine the dispersion density.

[0075] In the process, high temperature acts to provide sufficient activation energy for atomic diffusion and overcome the energy barrier for bond formation. As an example, when a single Pt atom escapes from a Pt-30 cluster to form a Pt-C bond, kinetically, there is an energy barrier (e.g., 1.48 eV) that prevents dispersion, which can be overcome at high temperatures (Figure 10, part (f) and Supplementary, Figure S12). HTHP dispersion at other temperatures can also be simulated: 500 K, 1000 K, 2000 K, and 2500 K (Supplementary, Figure S13). Although similar HTHP heating pulse patterns (on / off ratios and number of cycles) were applied, temperatures of 500 K and 1000 K failed to completely disperse the Pt cluster within a given repeated cycle. In contrast, higher HTHP heating pulse temperatures have improved kinetics and can achieve monoatomic dispersion much faster, i.e., much higher dispersion efficiency (Figure 10, part (g)). Furthermore, the Pt-C bond distribution in these monoatomic nanoparticles shows an increase in the proportion of more stable 5-10 type bonds at higher synthesis temperatures, indicating improved thermal stability (Figure 10, part (h)). Thus, high temperature synthesis for monoatomic dispersion and stabilization provides activation energy, accelerating the dispersion process and promoting more stable bond formation. For clarity, it should be noted that the monoatomic dispersion achieved by the HTHP process does not disperse all clusters and some clusters may remain after the HTHP process.

[0076] The above paragraphs describe the application of the HTHP process to synthesize Pu atoms. The HTHP synthesis process can generally be applied to other metals and substrates, where high temperature enables atomic dispersion by forming stable metal-defect bonds, while HTHP pulse heating helps to maintain the overall stability. Since the HTHP temperature is high enough compared to the pyrolysis temperature of most metal precursors, the HTHP process can be used to generate monoatomic dispersions of most metals, including Ru and Co monoatoms on CA-CNF, which is addressed in Figure 11 and Supplementary, Figure S14.

[0077] Figure 11 shows graphs and images of the application of the HTHP process to various atoms and substrates as well as for various applications. Part (a) shows the Co monoatom synthesized on CA-CNF confirmed by EXAFS profile and HAADF image (inset). Parts (b) and (c) show the Pt monoatom synthesized on C3N4 and TiO2 substrates through radiative and conductive shock wave synthesis (~0.5 wt%). Part (d) shows the light-off curve and part (e) shows the Arrhenius plot of Pt monoatom for CO oxidation reaction before and after water steam treatment at 973 K for 4 h, showing stable performance after hydrothermal treatment. Part (f) shows the stable performance of Pt monoatom during CO oxidation at 493 K for 50 h. Part (g) shows high temperature direct CFC conversion at 973 K for 50 h by Pt monoatom and Pt IMP sample. Part (h) shows the reaction turnover frequency (TOF) compared to the literature.

[0078] Furthermore, still in reference to Figure 11, the shock wave method can be extended and applied to other substrates, e.g., conductive reduced graphene oxide, semiconducting C3N4, and oxides such as TiO2, but using different heating methods (Supplementary, Figure S15) and forming different bonds with the substrate (Supplementary, Figure S16). Radiative HTHP heating can be used for powder samples by depositing the precursor-loaded powder under a carbon film that can be Joule heated with a HTHP pulse pattern. The high temperatures achieved in the film also heat the C3N4 powder and induce a dense monoatomic dispersion (Figure 11, part (b)). In addition, HTHP pulse heating maintains the structural integrity of C3N4, which is easily carbonized by prolonged heating (Supplementary, Figure S17). Non-contact radiative heating can also be scaled up for continuous production (Figure 8, and Supplementary, Figure S18). Alternatively, Pt monoatomic dispersion on TiO2 substrates can be achieved by depositing a thin layer (~2.5 nm) of TiO2 on the nanofibers in CA-CNF membranes via atomic layer deposition, since oxides have poor thermal conductivity for effective radiative heating (Supplementary Fig. S15c). Also, HTHP pulse heating of CA-CNF membranes heats the TiO2 layer through conductive heating and induces monoatomic dispersion on TiO2 (Fig. 11, part (c)). These results demonstrate the general applicability of the HTHP process for synthesizing thermally stable monoatomic dispersions, which suggests great potential for scalable nanofabrication.

[0079] To test the stability of the HTHP-synthesized single atoms, we performed 10- 3In situ hydrothermal tests could be performed for Pt monoatoms on CA-CNFs at HO partial pressures of mbar, with each test temperature held for at least 30 min. As shown in the Supplementary Figure S19, there were no nanoclusters appearing during in situ measurements up to 773 K, demonstrating that the HTHP-synthesized monoatoms are stable. Furthermore, the performance stability of Pt HT-SA in the CO oxidation reaction before and after hydrothermal treatment at 973 K for 4 h with 5% HO could be confirmed, supporting the hydrothermal stability of Pt monoatoms (Figure 11, part (d)). The Arrhenius plot (Figure 11, part (e), measured by kinetic studies) shows that the apparent reaction energies of the Pt monoatom catalyst before and after steam pretreatment are very close (50.7 kJ / mol vs. 53.2 kJ / mol). Furthermore, multiple cycles of CO oxidation measurements (Supplementary, Figure S20) as well as a stability test at 493 K for 50 h confirm the high stability of the Pt single atom (Figure 11, part (f)).

[0080] Furthermore, we can demonstrate the HTHP-synthesized single atom for reductive catalytic application of direct methane conversion, where the single atom catalyst shows good performance due to coke resistance by preventing catalytic C-C coupling. A comparative control sample can be synthesized by conventional impregnation (i.e., IMP) method using the same material but by thermal reduction at 573 K for 1 h (Supplementary, Figure S21). Figure 11, part (g) and Supplementary, Figure S22 show the Pt IMP (T) for direct CH4 to various products such as ethylene, ethane, propylene, propane, butene, and benzene at 973 K. s = 573 K) and HTHP-synthesized Pt single atom (T s = 1500 K) across all hydrocarbon products. The product distribution is C2H4, C2H6, and C6H GThe results showed high selectivity (>90%) for CH4 and no coke formation. In contrast, the Pt IMP sample showed intense coke formation even during the first hour of reaction, which could be attributed to the continuous assembly and aggregation of Pt sites at high temperature (973 K). Part (h) of Figure 11 shows the excellent stability of HTHP-synthesized Pt single atoms in CH4 conversion with a stable turnover frequency (TOF) of 50 h, in contrast to the rapid decrease in TOF of the Pt IMP sample due to its dispersion instability at high temperature. The HTHP-synthesized single atoms showed approximately 1000 times higher TOF than Pt nanoclusters deposited on SiO2 catalyst reported in the literature under similar conditions, revealing the high efficiency of single atom catalysts. Such practical results demonstrate the excellent thermal stability of single atoms synthesized by the HTHP process and their great potential for catalytic applications.

[0081] Referring now to FIG. 12, diagrams and images are shown for the formation of Pt-Ru biatomics on carbon nanofibers by HTHP process. Part (a) shows simulation efforts showing the dispersion of Pt-Ru into monoatoms and the formation of bimetallic alloy. Part (b) shows a high-resolution image of the atomic dispersion of Pt-Ru biatomics without obvious segregation. Part (c) shows the X-ray absorption profile of Pt edge and Ru edge, showing that Pt-Ru in Pt-Ru biatomics is different from individual metal foils, indicating the formation of Pt-Ru alloy bond.

[0082] Figure 13 shows high resolution atomic images of the formation of diatomic clusters on carbon and C3N4 substrates by the HTHP process. Part (a) shows the diatomic dispersion of Pt-Co on carbon nanofibers (CNFs). Part (b) shows the diatomic dispersion of Pt-Fe on reduced graphene oxide (RGO). Part (c) shows the diatomic dispersion of Pt-Co on C3N4 substrates. No cluster formation is evident in each image / sample.

[0083] Thus, the present disclosure provides a high temperature heating pulse process for synthesizing monoatomic and polyatomic dispersions on a substrate. The high temperature pulse acts to disperse the clusters and synthesize monoatomic dispersions on the substrate. The monoatoms are stabilized by defects on the substrate and by bonds with the substrate. For clarity, it is noted that the monoatomic dispersion achieved by the HTHP process does not disperse all clusters, and some clusters may remain after the HTHP process.

[0084] The HTHP pulse configuration and pattern are flexible and can be used to high ), low temperature (T low ), heating duration (t high ), cooling duration (t low ), heating rate (R heating ), cooling rate (R cooling ), and the number of cycles (n) can be varied independently for the HTHP process.

[0085] Heating configurations are also flexible and can include, but are not limited to, direct Joule heating, conductive heating, radiative heating, microwave heating, laser heating, and / or plasma heating, as shown in Figures 3, 8, and 14. Also, different cooling processes can be implemented, including, but are not limited to, cooling by radiation and conduction, active cooling by conduction and convection, and / or active cooling by physical or chemical transitions that absorb heat.

[0086] Polyatomic groups / atomic alloys can be formed by sequential / iterative application of the HTHP process, which allows monoatomic dispersion of one species at a time. In such a process, the atoms in the polyatomic groups can be different or the same, and can be pure metals or their compounds. The substrate can be carbon-based materials, metals, ceramics, polymers, composites, oxides, and / or combinations thereof.

[0087] Common atomic alloys with different element combinations can be synthesized by successively applying the HTHP process with different elements in each iteration. In this method, the single atoms can be any element that can be dispersed into atomic form, including their compound formation. The substrate can be a carbon-based material, a metal, a ceramic, a polymer, a composite, an oxide, and / or a combination thereof.

[0088] The synthesized monoatomic and polyatomic groups / alloys can be used in many different applications, including but not limited to thermochemical, electrochemical, and photochemical catalysis. Also, the synthesis of monoatomic and polyatomic alloys can be used for fundamental research in atomic manipulation.

[0089] The embodiments disclosed herein are examples of the disclosure and may be embodied in various forms. For example, although certain embodiments herein are described as separate embodiments, each of the embodiments herein may be combined with one or more of the other embodiments herein. The specific structural and functional details disclosed herein should not be interpreted as limitations, but as a basis for claims and as a representative basis for teaching those skilled in the art to use the present disclosure in various ways in substantially any appropriately detailed structure. Throughout the description of the drawings, similar reference numbers may refer to similar or identical elements.

[0090] The phrases "in one embodiment," "in embodiments," "various embodiments," "in some embodiments," or "in other embodiments" can each refer to one or more of the same or different embodiments according to the disclosure. The phrase "A or B" means "(A), (B), or (A and B)." The phrase "at least one of A, B, or C" means "(A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C)."

[0091] It should be understood that the foregoing description is merely illustrative of the present disclosure. Those skilled in the art may conceive of various alternatives and modifications without departing from the present disclosure. Accordingly, the present disclosure is intended to embrace all such alternatives, modifications, and variations. The embodiments described with reference to the accompanying drawings are presented only to demonstrate certain examples of the present disclosure. The embodiments described and illustrated herein are exemplary, and variations are considered to be within the scope of the present disclosure. The various embodiments disclosed herein may be combined in ways not expressly described herein, and such combinations are considered to be within the scope of the present disclosure. Other elements, steps, methods, and techniques that are substantially different from those described above and / or in the appended claims are also intended to be within the scope of the present disclosure.

Claims

1. Positioning a substrate loaded with at least one of a precursor of a first metal or clusters of said first metal; applying a plurality of first heating cycles to the loaded substrate, where each of the first heating cycles includes a first temperature pulse applied to the loaded substrate for a first duration; the duration is followed by a first cooling period; each first temperature pulse applies a temperature of 500 K or more and 4000 K or less via direct Joule heating, conductive heating, radiative heating, microwave heating, laser heating, or plasma heating; each first duration is greater than or equal to 1 millisecond and less than or equal to 1 minute; cooling in each first cooling period includes cooling by radiation and conduction, active cooling by conduction and convection, or active cooling by physical or chemical transitions that absorb heat; The substrate comprises a carbon-based material or an oxide, after applying a plurality of first heating cycles, a plurality of individual monoatoms of the first metal are separately dispersed and bonded onto the substrate; A method for synthesizing an atomic dispersion comprising:

2. loading at least one of a precursor of a second metal or clusters of the second metal onto the substrate after applying a plurality of first heating cycles; applying a plurality of second heating cycles to the loaded substrate, each second heating cycle including a second temperature pulse applied to the loaded substrate for a second duration, the second duration being followed by a second cooling period; Each of the second temperature pulses applies a temperature of 500 K or more and 4000 K or less; after applying a plurality of said second heating cycles, a plurality of individual monoatoms of said second metal are dispersed on said substrate. The method of claim 1.

3. after applying each of the second heating cycles, a plurality of individual monoatoms of the second metal are bonded with each of the individual monoatoms of the first metal to form diatomic dispersions. The method of claim 2.

4. each of the first metal atoms and the second metal atoms being bonded to the substrate after being subjected to a plurality of heating cycles; The method of claim 2.

5. The first metal atom and the second metal atom are the same element. The method of claim 2.

6. the first metal atom and the second metal atom are different elements; The method of claim 2.

7. loading at least one of a precursor of a third metal or clusters of the third metal onto the substrate after applying a plurality of second heating cycles; applying a plurality of third heating cycles to the loaded substrate, each third heating cycle including a third temperature pulse applied to the loaded substrate for a third duration, the third duration being followed by a third cooling period; Each of the third temperature pulses applies a temperature of 500 K or more and 4000 K or less; after applying a plurality of said third heating cycles, a plurality of individual monoatoms of said third metal are dispersed on said substrate. The method of claim 2.

8. after applying a plurality of first heating cycles, the substrate has a uniform distribution of individual monoatoms of the first metal. The method of claim 1.

9. the first metal is one of Pt, Ru, or Co; The method of claim 1.

10. the substrate includes a plurality of defects; after applying a plurality of first heating cycles, the defects act to stabilize individual monoatoms of the first metal on the substrate. The method of claim 1.

11. The substrate is made of carbon nanofibers, C 3 N 4 , TiO 2 or reduced graphene oxide, The method of claim 1.

12. The substrate is 2 Activated carbon nanofibers, The method of claim 1.

13. Prior to applying a plurality of the first heating cycles, the loading of the first metal precursor or the first metal clusters on the loaded substrate is greater than or equal to 0.05 μmol / cm 2 Less The method of claim 1.

14. Prior to applying a plurality of the first heating cycles, the loading of the precursor of the first metal or the clusters of the first metal on the loaded substrate is greater than or equal to 0.005 μmol / cm 2 ~0.01μmol / cm 2 In the range of The method of claim 1.

15. the duration of the first cooling period is ten times the duration of the first cooling period; and / or the number of said first heating cycles is between 2 and 10; The method of claim 1.

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