Transition metal loaded and heteroatom doped carbon material and preparation method thereof

Abstract

The invention discloses a transition metal loaded and heteroatom doped carbon material and a preparation method thereof. The preparation method comprises the following steps: S1, providing a carbon substrate; s2, performing heteroatom doping on the carbon substrate in a vacuum cavity; s3, loading transition metal particles on the surface of the heteroatom-doped carbon substrate in a vacuum cavity to obtain a transition metal loaded and heteroatom-doped carbon material; and S4, carrying out heat treatment on the transition metal loaded and heteroatom doped carbon material in the vacuum cavity. By optimizing transition metal loading and heteroatom doping processes, the doped carbon material with a uniform structure can be prepared, and the loading capacity, the valence state, the dispersity and the catalytic performance can be regulated and controlled.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a transition metal loaded and heteroatom doped carbon material and a preparation method thereof. Background Art

[0002] In recent years, transition metal catalysts supported on carbon materials have been widely used in the field of energy catalysis. This is mainly due to the high specific surface area, good conductivity and easily adjustable defect sites of carbon materials, which can fully disperse and anchor metal atoms, maximize the catalyst dispersion and metal utilization, and reduce the catalyst cost. The coordinated unsaturated carbon atoms on the surface and edge of nanoscale carbon materials have obvious localized electrons. These topological defects (point defects) and edge carbon atoms (line defects) are easy to bond with other heteroatoms (O, N, S, etc.), thus forming a new localized electronic environment. Using heteroatom doping methods to regulate carbon material carriers is one of the current research hotspots. On the surface of heteroatom-doped carbon materials, the introduction of coordinated transition metals can construct atomically dispersed metal catalytic materials. The presence of heteroatoms achieves a stronger anchoring effect on metal atoms. At the same time, the interaction between heteroatoms and metals is used to effectively regulate the electronic structure of the active center metal to improve its catalytic performance.

[0003] Existing technologies for synthesizing doped carbon materials can be roughly divided into two categories: one is to mix the carbon source with the heteroatom precursor salt in the precursor and then perform heat treatment; the other is to dope the already synthesized carbon material using a post-treatment process. There are multiple types of defect sites and heteroatoms on the surface of the obtained carbon material, and the spatial position of the doping is completely disordered and uncontrollable. Using it as a carrier usually produces catalytic materials with multiple active sites coexisting, such as metal nanoparticles, sub-nanoclusters, and single atoms with different morphologies, sizes, and coordination environments, which increases the difficulty of establishing the structure-activity relationship of the system and identifying the catalytic active centers.

[0004] Therefore, in order to solve the above technical problems, it is necessary to provide a transition metal loaded and heteroatom doped carbon material and a preparation method thereof. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a transition metal loaded and heteroatom doped carbon material and a preparation method thereof.

[0006] In order to achieve the above purpose, the technical solution provided by an embodiment of the present invention is as follows:

[0007] A method for preparing a transition metal loaded and heteroatom doped carbon material, the preparation method comprising the following steps:

[0008] S1. providing a carbon substrate;

[0009] S2, in a vacuum chamber, performing heteroatom doping on the carbon substrate;

[0010] S3, in a vacuum chamber, loading transition metal particles on the surface of a heteroatom-doped carbon substrate to obtain a transition metal-loaded and heteroatom-doped carbon material;

[0011] S4. In a vacuum chamber, heat-treating the transition metal loaded and heteroatom doped carbon material.

[0012] In one embodiment, the coverage of the heteroatoms is 0.1 ML to 0.5 ML, and the coverage of the transition metal particles is 0.1 ML to 0.5 ML.

[0013] In one embodiment, the carbon substrate is any one of HOPG, carbon cloth, and carbon paper; and / or,

[0014] The heteroatom is any one or more of an oxygen atom, a nitrogen atom, a hydrogen atom, and an argon atom; and / or,

[0015] The transition metal particles are any one or more of single atoms, sub-nano clusters, and nanoparticles, and the material of the transition metal particles is any one or more of tungsten, platinum, palladium, nickel, iron, copper, gold, and silver.

[0016] In one embodiment, in step S2, the carbon substrate is doped with heteroatoms by a plasma treatment process. In the plasma treatment process, the background vacuum degree of the vacuum chamber is less than or equal to 1×10 -9 mbar, gas pressure is 1×10 - 8 mbar~1mbar, power is 5W~20W, and processing time is 20s~10min.

[0017] In one embodiment, in step S3, transition metal particles are loaded on the surface of the heteroatom-doped carbon substrate by an atomic layer deposition process, an electrodeposition process, or a physical vapor deposition process.

[0018] In one embodiment, the annealing temperature of the heat treatment in step S4 is 300°C to 700°C.

[0019] In one embodiment, at least one pretreatment process is further included before step S2, and the pretreatment process includes vacuum annealing at a temperature of 500°C to 1000°C.

[0020] In one embodiment, the pretreatment process further includes Ar ion etching, the etching gas is argon gas, and the ion energy is 0.1 keV to 1 keV.

[0021] In one embodiment, the preparation method further comprises:

[0022] Characterizing the surface morphology of the carbon substrate after the pretreatment process in an STM device; and / or,

[0023] In situ characterization of the transition metal particle loaded carbon material in an XPS instrument; and / or,

[0024] The heat-treated carbon materials were characterized in situ in the XPS equipment.

[0025] Another embodiment of the present invention provides a technical solution as follows:

[0026] A transition metal loaded and heteroatom doped carbon material is prepared by the above-mentioned preparation method.

[0027] The present invention has the following beneficial effects:

[0028] The transition metal-loaded and heteroatom-doped carbon material of the present invention is prepared in a vacuum interconnected system, which effectively avoids the problem of the carbon substrate reacting and bonding with water and oxygen in the air during the transfer process, and can obtain a high-purity transition metal-loaded and heteroatom-doped carbon material;

[0029] By in situ characterization of transition metal loaded and heteroatom doped carbon materials after transition metal particle loading and heat treatment, the structure of transition metal loaded and heteroatom doped carbon materials can be controlled, thereby improving the quality and preparation efficiency of transition metal loaded and heteroatom doped carbon materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 It is a structural schematic diagram of the vacuum interconnection system in the present invention;

[0032] Figure 2 is a schematic diagram of surface defects of the heteroatom-doped carbon material in Comparative Example 1 of the present invention;

[0033] Figure 3 is an STM image of nitrogen-doped graphene grown on the surface of a Cu single crystal substrate in Comparative Example 2 of the present invention;

[0034] Figure 4 1 is a schematic flow chart of the method for preparing a transition metal-loaded and heteroatom-doped carbon material in Example 1 of the present invention;

[0035] Figure 5 are STM images of the surface of the HOPG substrate after pretreatment in Example 1 of the present invention at different magnifications;

[0036] Figure 6 is an STM image of the surface of O-HOPG after oxygen plasma treatment in Example 1 of the present invention;

[0037] Figure 7 1 is an STM image of W / O-HOPG loaded with tungsten particles at different magnifications in Example 1 of the present invention;

[0038] Figure 8 is the XPS spectrum of W / O-HOPG loaded with tungsten particles in Example 1 of the present invention;

[0039] Fig. 9 is an STM image of the surface of O-HOPG after oxygen plasma treatment in Example 2 of the present invention;

[0040] Fig.10 It is a comparison chart of the alkaline HER performance of W / O-HOPG prepared by different heat treatment methods in the present invention.

[0041] Description of reference numerals:

[0042] 1-glove box, 2-vacuum chamber, 3-XPS, 4-preparation chamber, 5-STM. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0044] The present invention discloses a method for preparing a transition metal loaded and heteroatom doped carbon material, comprising the following steps:

[0045] S1. providing a carbon substrate;

[0046] S2, in a vacuum chamber, performing heteroatom doping on the carbon substrate;

[0047] S3, in a vacuum chamber, loading transition metal particles on the surface of a heteroatom-doped carbon substrate to obtain a transition metal-loaded and heteroatom-doped carbon material;

[0048] S4. In a vacuum chamber, heat-treating the transition metal loaded and heteroatom doped carbon material.

[0049] Ginseng Figure 1 As shown, the present invention adopts a vacuum interconnection system consisting of a glove box 1, a vacuum chamber 2, a preparation chamber 4, an X-ray photoelectron spectroscopy analysis (XPS) 3 and a scanning tunneling microscope (STM) 5 to prepare transition metal-loaded and heteroatom-doped carbon materials. Adjacent equipment is interconnected by vacuum interconnection pipes, and the vacuum chamber is equipped with a plasma reactor and a molecular pump-mechanical pump group.

[0050] The present invention is further described below with reference to specific examples.

[0051] Comparative Example 1:

[0052] Ginseng Figure 2 Shown is a schematic diagram of the surface defects of the heteroatom-doped carbon material in this comparative example. In this comparative example, there are multiple heteroatoms on the surface of the carbon material after heteroatom doping and have multiple different doping structures. When such heteroatom-doped carbon material is used as a substrate to load transition metal particles, the transition metal particles have multiple landing structures, making it difficult to accurately obtain the structure-activity relationship of the catalytic system.

[0053] Comparative Example 2:

[0054] Ginseng Figure 3 This is an STM image of nitrogen-doped graphene grown on the surface of a Cu single crystal substrate in this comparative example. In this comparative example, by adjusting the vacuum annealing temperature, the amine groups on the graphene surface can be desorbed at a specific temperature while the pyridinic nitrogen exists stably, thereby ensuring that the nitrogen atoms on the graphene surface are all pyridinic nitrogen. At the same time, the nitrogen-doped graphene grown on the surface of a Cu single crystal substrate in this comparative example is prepared in an ultra-high vacuum chamber, and no other heteroatoms exist on the graphene surface.

[0055] In the research system of this comparative example, the metal single crystal substrate contributes part of the catalytic activity, making it difficult to characterize the intrinsic catalytic performance of the doped carbon material.

[0056] Embodiment 1:

[0057] Ginseng Figure 4 As shown, the preparation method of the transition metal and heteroatom doped carbon material in this embodiment specifically includes the following steps:

[0058] S1. Provide a carbon substrate.

[0059] The carbon substrate is any one of HOPG, carbon cloth, and carbon paper. Preferably, the carbon substrate in this embodiment is a highly oriented pyrolytic graphite (HOPG) substrate to facilitate surface morphology characterization in an STM device.

[0060] In this embodiment, the HOPG substrate is first pretreated, and the pretreatment process includes at least one vacuum annealing, and the annealing temperature is 500° C. to 1000° C.

[0061] Furthermore, for the HOPG substrate obtained by cleavage in the atmospheric environment, ion beam etching is required before vacuum annealing, the etching gas is argon gas, and the ion energy is 0.1 keV to 1 keV.

[0062] Specifically, in this embodiment, the cleaved HOPG substrate is first ion-beam etched, the etching gas is argon, the ion energy is 0.2 keV, and the argon partial pressure is 1×10 -6 mbar, the etching time is 2 min, and then the HOPG is vacuum annealed at a temperature of 500 °C for 30 min.

[0063] Furthermore, the pretreated carbon substrate is transferred into the STM device through a vacuum interconnection pipeline for surface morphology characterization.

[0064] Ginseng Figure 5 As shown, an atomically flat and clean HOPG substrate surface was obtained after ion beam etching and vacuum annealing.

[0065] S2. In a vacuum chamber, the carbon substrate is doped with heteroatoms.

[0066] The heteroatom in this embodiment is any one or more of oxygen atom, nitrogen atom, hydrogen atom and argon atom, and the coverage is 0.1ML to 0.5ML.

[0067] Exemplarily, the heteroatom in this embodiment is an oxygen atom, and the coverage is 0.2 ML.

[0068] Furthermore, in this embodiment, the carbon substrate is doped with heteroatoms by a plasma treatment process. In the plasma treatment process, the background vacuum degree of the vacuum chamber is less than or equal to 1×10 -9 mbar, gas pressure is 1×10 -8 mbar~1mbar, power is 5W~20W, and processing time is 20s~10min.

[0069] Specifically, the background vacuum degree of the vacuum chamber in the plasma treatment process in this embodiment is 1×10 -9 mbar, oxygen partial pressure is 0.1 mbar, power is 10 W, and processing time is 120 s.

[0070] Furthermore, the oxygen atom-doped HOPG substrate (O-HOPG) was transferred into the STM device through a vacuum interconnection pipeline for morphological characterization.

[0071] Ginseng Figure 6As shown, the obtained oxygen atom-doped HOPG substrate has oxygen atom doping that is substantially confined to the surface and subsurface regions of the HOPG substrate, has a high oxygen atom doping concentration, and has a coverage of 0.2 ML.

[0072] S3. In a vacuum chamber, loading transition metal particles on the surface of a heteroatom-doped carbon substrate to obtain a transition metal-loaded and heteroatom-doped carbon material.

[0073] The transition metal particles in this embodiment are any one or more of single atoms, sub-nano clusters, and nanoparticles. The material of the transition metal particles is any one or more of tungsten, platinum, palladium, nickel, iron, copper, gold, and silver, and the coverage is 0.1ML to 0.5ML.

[0074] Exemplarily, the material of the transition metal particles in this embodiment is tungsten.

[0075] Furthermore, in this embodiment, transition metal particles are loaded on the surface of the heteroatom-doped carbon substrate by an atomic layer deposition process, an electrodeposition process or a physical vapor deposition process.

[0076] For example, in this embodiment, tungsten particles are loaded on the surface of the oxygen-doped HOPG substrate by an atomic layer deposition process, and the partial pressure of the tungsten source is 1×10 -8 mbar~1×10 -7 mbar, and the coverage of tungsten particles can be adjusted by controlling the introduction time of the tungsten source.

[0077] Specifically, bis(tert-butylimino)bis(dimethylamino)tungsten was selected as the tungsten source and introduced into the vacuum chamber. The partial pressure of the tungsten source was 1×10 -7 mbar, the introduction time was 10 s, and the tungsten particles were loaded on the oxygen atom-doped HOPG substrate to obtain tungsten-loaded and oxygen-doped HOPG (W / O-HOPG).

[0078] S4. In a vacuum chamber, heat-treating the transition metal loaded and heteroatom doped carbon material.

[0079] The heat treatment in this embodiment is performed in a hydrogen atmosphere, and the hydrogen partial pressure is 1×10 -7 mbar~10mbar, the heat treatment temperature is 300℃~700℃, and the chemical valence state of the transition metal particles loaded in the obtained transition metal-loaded and heteroatom-doped carbon materials is regulated by adjusting the hydrogen partial pressure and the annealing temperature.

[0080] Specifically, in this embodiment, the hydrogen partial pressure is 0.1 mbar, the annealing temperature is 500° C., and the annealing time is 10 min.

[0081] Furthermore, the surface morphology of the W / O-HOPG loaded with tungsten particles was characterized in an STM device.

[0082] Ginseng Figure 7 As shown in FIG. 1 , the average particle size of the tungsten particles in the W / O-HOPG prepared by the above preparation method is 3 nm, and the average height is

[0083] Furthermore, the W / O-HOPG with tungsten particle loading was in-situ characterized in an XPS device.

[0084] Ginseng Figure 8 As shown, the chemical valence state of the tungsten particles in the W / O-HOPG prepared by the above preparation method indicates that there is obvious electron transfer between the tungsten particles and O-HOPG.

[0085] Embodiment 2:

[0086] The preparation method of O-HOPG in this embodiment is substantially the same as the preparation method of O-HOPG in Example 1, except that the treatment time of the plasma treatment process is 30 s.

[0087] Ginseng Fig. 9 As shown, compared with Example 1, the oxygen atom doping concentration on the surface of the HOPG substrate with a treatment time of 30 s is lower, and the coverage is about 0.1 ML.

[0088] Embodiment 3:

[0089] The preparation method of W / O-HOPG in this example is substantially the same as that in Example 1, except that the W / O-HOPG in this comparative example is not subjected to heat treatment.

[0090] Embodiment 4:

[0091] The preparation method of W / O-HOPG in this embodiment is roughly the same as that in Example 1, except that the hydrogen partial pressure during the heat treatment is 1×10 -6 mbar, and the annealing temperature is 300°C.

[0092] Embodiment 5:

[0093] The preparation method of W / O-HOPG in this embodiment is substantially the same as that in Embodiment 1, except that the hydrogen partial pressure during heat treatment is 0.1 mbar and the annealing temperature is 700°C.

[0094] Embodiment 6:

[0095] The preparation method of W / O-HOPG in this embodiment is substantially the same as that in Embodiment 1, except that the hydrogen partial pressure during heat treatment is 1 mbar and the annealing temperature is 700°C.

[0096] Ginseng Fig.10 The figure shows a comparison of the alkaline HER performance of W / O-HOPG prepared by different heat treatment methods, wherein 1 is the alkaline HER performance curve of W / O-HOPG in Example 1, 2 is the alkaline HER performance curve of W / O-HOPG in Example 3, 3 is the alkaline HER performance curve of W / O-HOPG in Example 4, 4 is the alkaline HER performance curve of W / O-HOPG in Example 5, and 5 is the alkaline HER performance curve of W / O-HOPG in Example 6. The alkaline HER performance of W / O-HOPG in Example 1 is the best, and the alkaline HER performance of W / O-HOPG in Example 3 is the worst.

[0097] Compared with Example 1, Example 4 adopts a lower annealing temperature and a lower hydrogen reduction temperature, which cannot fully reduce the tungsten precursor.

[0098] Compared with Example 1, Examples 5 and 6 use a higher annealing temperature and a hydrogen reduction temperature that is too high, causing the surface tungsten particles to agglomerate and thus failing to obtain a high dispersion of active components.

[0099] It can be seen from the above technical solution that the present invention has the following beneficial effects:

[0100] The transition metal-loaded and heteroatom-doped carbon material of the present invention is prepared in a vacuum interconnected system, which effectively avoids the problem of the carbon substrate reacting and bonding with water and oxygen in the air during the transfer process, and can obtain a high-purity transition metal-loaded and heteroatom-doped carbon material;

[0101] By in-situ characterization of transition metal loaded and heteroatom doped carbon materials after transition metal loading and heat treatment, the structure of transition metal loaded and heteroatom doped carbon materials can be controlled, thereby improving the quality and preparation efficiency of transition metal loaded and heteroatom doped carbon materials.

[0102] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0103] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing a transition metal loaded and heteroatom doped carbon material, characterized in that: The preparation method comprises the following steps: S1. providing a carbon substrate; S2, in a vacuum chamber, performing heteroatom doping on the carbon substrate; S3, in a vacuum chamber, loading transition metal particles on the surface of a heteroatom-doped carbon substrate to obtain a transition metal-loaded and heteroatom-doped carbon material; S4. In a vacuum chamber, heat-treating the transition metal loaded and heteroatom doped carbon material.

2. The method for preparing a transition metal-loaded and heteroatom-doped carbon material according to claim 1, characterized in that: The coverage of the heteroatoms is 0.1ML to 0.5ML, and the coverage of the transition metal particles is 0.1ML to 0.5ML.

3. The method for preparing a transition metal-loaded and heteroatom-doped carbon material according to claim 1, characterized in that: The carbon substrate is any one of HOPG, carbon cloth, and carbon paper; and / or, The heteroatom is any one or more of an oxygen atom, a nitrogen atom, a hydrogen atom, and an argon atom; and / or, The transition metal particles are any one or more of single atoms, sub-nano clusters, and nanoparticles, and the material of the transition metal particles is any one or more of tungsten, platinum, palladium, nickel, iron, copper, gold, and silver.

4. The method for preparing a transition metal loaded and heteroatom doped carbon material according to claim 1, characterized in that: In step S2, the carbon substrate is doped with heteroatoms by a plasma treatment process. In the plasma treatment process, the background vacuum degree of the vacuum chamber is less than or equal to 1×10 -9 mbar, gas pressure is 1×10 -8 mbar~1mbar, power is 5W~20W, and processing time is 20s~10min.

5. The method for preparing a transition metal loaded and heteroatom doped carbon material according to claim 1, characterized in that: In the step S3, transition metal particles are loaded on the surface of the heteroatom-doped carbon substrate by using an atomic layer deposition process, an electrodeposition process or a physical vapor deposition process.

6. The method for preparing a transition metal loaded and heteroatom doped carbon material according to claim 1, characterized in that: The annealing temperature of the heat treatment in step S4 is 300°C to 700°C.

7. The method for preparing a transition metal loaded and heteroatom doped carbon material according to claim 1, characterized in that: The step S2 further includes at least one pretreatment process, wherein the pretreatment process includes vacuum annealing at a temperature of 500° C. to 1000° C.

8. The method for preparing a transition metal loaded and heteroatom doped carbon material according to claim 7, characterized in that: The pretreatment process also includes ion beam etching, the etching gas is argon gas, and the energy of the generated argon ions is 0.1 keV to 1 keV.

9. The method for preparing a transition metal loaded and heteroatom doped carbon material according to claim 7, characterized in that: The preparation method further comprises: Characterizing the surface morphology of the carbon substrate after the pretreatment process in an STM device; and / or, In situ characterization of the transition metal particle loaded carbon material in an XPS instrument; and / or, The heat-treated carbon materials were characterized in situ in the XPS equipment.

10. A transition metal loaded and heteroatom doped carbon material, characterized in that: The transition metal-loaded and heteroatom-doped carbon material is prepared by the preparation method according to any one of claims 1 to 9.

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