A diatomic metal electrocatalyst, and a preparation method and application thereof
A high-density diatomic metal electrocatalyst was prepared by sublimating anhydrous ferric chloride and aluminum in nitrogen-doped carbon materials, solving the preparation problem in the prior art and achieving high efficiency and stability in the electrocatalytic oxygen reduction reaction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING UNIV OF CHEM TECH
- Filing Date
- 2023-08-02
- Publication Date
- 2026-07-21
AI Technical Summary
Existing technologies make it difficult to prepare high-density and well-dispersed diatomic catalysts easily and accurately, which limits catalytic efficiency, especially in electrocatalytic oxygen reduction reactions.
Anhydrous ferric chloride and anhydrous aluminum chloride are sublimated on nitrogen-doped carbon materials to form metal chloride dimers. High-proportion, uniformly loaded diatomic metal electrocatalysts are obtained through heat treatment. Nitrogen-doped carbon materials are used as conductive substrates to enhance the interaction between the metal and the support.
The high efficiency of the diatomic metal electrocatalyst in the oxygen reduction reaction was achieved, with a half-wave potential superior to that of commercial Pt/C catalysts, and better stability and selectivity in alkaline environments.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrocatalysis, specifically relating to a diatomic metal electrocatalyst, its preparation method, and its application. Background Technology
[0002] Single-atom catalysts, with their near 100% atomic utilization, unsaturated coordination environment, and unique electronic structure, have been proven to improve catalytic activity, selectivity, and stability in various reactions. However, the linear proportionality between the adsorption strength of different reaction intermediates at a single atom active site is difficult to break, limiting the improvement of their catalytic efficiency. Furthermore, single-atom catalysts typically employ low metal loading to prevent aggregation, which also significantly restricts their practical application. Diatom catalysts with adjacent bimetallic atomic sites are considered an extension of single-atom catalysts, offering a feasible strategy to address the aforementioned problems. While maintaining the advantages of single-atom catalysts, diatomic catalysts exhibit a more flexible active site structure and hold promise for higher metal loading. Diatom catalysts provide adjacent metal atom active sites for complex catalytic reactions (such as the electrocatalytic oxygen reduction reaction), enabling multiple binding modes of reactant / intermediate molecules and simultaneous binding of different molecules, increasing the possibilities of reaction pathways. Moreover, the synergistic effect between the two atoms can effectively modulate the electronic interactions between reactants / intermediates and the active site. These characteristics allow diatomic catalysts to break the linear proportionality of intermediate adsorption strength, thereby achieving improved catalytic activity and selectivity.
[0003] In recent years, diatomic catalysts have achieved some breakthroughs in the field of catalysis, becoming a hot research direction in nanocatalysis chemistry. However, a simple, precise, and controllable synthesis strategy for preparing diatomic catalysts is still lacking. High-temperature pyrolysis is a relatively simple and commonly used method, but it is usually carried out above 800℃, which can cause the aggregation of some metal atoms, thus affecting catalytic performance. Although some deposition techniques can effectively control the synthesis process, it is difficult to avoid the coexistence of a large number of single-atom sites, and they have high requirements for equipment and require strict control of testing conditions. In recent years, wet chemical synthesis methods have also become a focus of research, but this method usually uses low concentrations of metal precursors to ensure good atomic dispersion. In addition, the weak interaction between the metal center and the support is another problem of this method, which will affect the catalytic efficiency of the final catalyst.
[0004] Therefore, developing a simple, readily available, and well-dispersed diatomic catalyst with high catalytic performance is of great value and significance.
[0005] To address the above problems, this invention is proposed. Summary of the Invention
[0006] To address the problems existing in the background technology, the present invention aims to provide a diatomic metal electrocatalyst, its preparation method, and its application. This preparation method is based on the physical property that anhydrous ferric chloride and anhydrous aluminum chloride sublimate into metal chloride dimers within a certain temperature range. Using nitrogen-doped carbon material as a conductive substrate, and through steps such as adsorption and heat treatment, a diatomic metal electrocatalyst with a high proportion and uniform loading on the nitrogen-doped carbon material is obtained. The prepared catalyst can be applied to the electrocatalytic oxygen reduction reaction.
[0007] A first aspect of this invention provides a diatomic metal electrocatalyst, comprising: a conductive substrate, and a diatomic iron or diatomic aluminum supported on the conductive substrate, wherein the diatomic iron consists of two iron single atoms, the diatomic aluminum consists of two aluminum single atoms, and the distance between the two iron single atoms is less than or equal to 0.32 nm, and the distance between the two aluminum single atoms is less than or equal to 0.26 nm. More preferably, the distance between the two iron single atoms is 0.19–0.32 nm, and the distance between the two aluminum single atoms is 0.16–0.26 nm.
[0008] Preferably, the conductive substrate is a nitrogen-doped carbon material.
[0009] Preferably, the diatomic iron or the diatomic aluminum accounts for more than 70% of all atomic sites on the conductive substrate. More preferably, the diatomic iron accounts for 72.4% of all atomic sites on the conductive substrate, and the diatomic aluminum accounts for 75% of all atomic sites.
[0010] A second aspect of the present invention provides a method for preparing the diatomic metal electrocatalyst according to any one of the first aspects, comprising the following steps:
[0011] (1) Select one of anhydrous ferric chloride and anhydrous aluminum chloride as the metal precursor, and place the metal precursor and the conductive substrate horizontally or vertically in the heating device, and the placement position is such that the volatilized metal chloride dimer vapor can fully contact the conductive substrate.
[0012] The term "horizontal placement" refers to the metal precursor being upstream and the conductive substrate being downstream; here, upstream and downstream are defined by the direction of movement of the volatile metal chloride dimer vapor, which moves from upstream to downstream. The term "vertical placement" refers to the metal precursor being below and the conductive substrate being above.
[0013] (2) Start the heating device described in step (1), heat-treat the metal precursor and conductive substrate at a first temperature, carry out the volatilization and adsorption process of metal chloride dimer, and collect the conductive substrate that has adsorbed metal chloride dimer after naturally cooling to room temperature.
[0014] (3) The conductive substrate in step (2) that has adsorbed the metal chloride dimer is subjected to heat treatment under an inert or hydrogen atmosphere to obtain the diatomic metal electrocatalyst.
[0015] Preferably, in step (1), the conductive substrate is a nitrogen-doped carbon material containing nitrogen and having a high specific surface area.
[0016] Preferably, in step (1), the mass ratio of the anhydrous ferric chloride to the conductive substrate is 1:10 to 5:1.
[0017] Preferably, in step (2), when the metal precursor is anhydrous ferric chloride, the first temperature is 300-500°C; when the metal precursor is anhydrous aluminum chloride, the first temperature is 180-300°C.
[0018] Preferably, in step (2), the adsorption time is 1 to 3 hours.
[0019] Preferably, in step (3), the temperature for the reduction heat treatment under the inert atmosphere is 700-900℃ and the time is 1-3h; the hydrogen volume concentration for the reduction heat treatment under the hydrogen atmosphere is 2-10%, the temperature is 300-600℃, and the time is 1-3h.
[0020] The third aspect of the present invention provides the application of the diatomic metal electrocatalyst described in any one of the first aspects in oxygen reduction catalytic reactions.
[0021] The above technical solutions can be freely combined, provided they do not contradict each other.
[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:
[0023] (1) This invention provides for the first time a diatomic metal electrocatalyst with high density and good dispersion of diatomic sites, which exhibits excellent performance in oxygen reduction catalysis. In the diatomic metal electrocatalyst of this invention, the distance between the two iron single atoms is less than or equal to 0.32 nm, the distance between the two aluminum single atoms is less than or equal to 0.26 nm, and the diatomic iron or diatomic aluminum accounts for more than 70% of all atomic sites.
[0024] (2) Based on the property that anhydrous ferric chloride (FeCl3) and anhydrous aluminum chloride (AlCl3) sublimate as metal chloride dimers within a certain temperature range, this invention utilizes a nitrogen-doped carbon conductive substrate (NC) to adsorb ferric chloride dimers (Fe2Cl6) and aluminum chloride dimers (Al2Cl6), respectively. The resulting adsorbed samples are then subjected to high-temperature heat treatment under an inert / hydrogen atmosphere to remove chloride ligands, enhance the interaction between the metal and the support, and further adjust the coordination environment of the iron or aluminum diatoms, ultimately obtaining diatomic metal electrocatalysts (Fe2 / NC, Al2 / NC). The method of this invention can achieve a high proportion, stable and uniform dispersion of metal diatoms on the support.
[0025] The synthesis process of Fe2 and Al2 diatomic metal electrocatalysts provided by this invention is simple to operate and has a short preparation cycle. Moreover, the metal precursors used are non-precious metal salts - iron salts / aluminum salts, which have the advantage of low cost.
[0026] (3) This invention uses the electrocatalytic oxygen reduction reaction as a probe reaction to study the catalytic superiority of diatomic catalysts. Compared with single-atom metal electrocatalysts, the diatomic metal electrocatalysts prepared in this invention exhibit superior electrochemical oxygen reduction performance. Specifically, the Fe2 / NC electrocatalyst achieves a half-wave potential of 0.887 V vs. RHE in the four-electron oxygen reduction reaction, far exceeding the half-wave potential of 0.831 V vs. RHE for the Fe1 / NC electrocatalyst, and even surpassing the half-wave potential of 0.871 V vs. RHE for commercial 20wt% Pt / C. Furthermore, the Fe2 / NC electrocatalyst exhibits superior stability compared to commercial 20wt% Pt / C; after 5000 potential cycles in an alkaline environment, its half-wave potential only decreases by 5 mV, while the half-wave potential of Pt / C decreases by nearly 30 mV. The Al2 / NC electrocatalyst exhibits outstanding H2O2 selectivity in the two-electron oxygen reduction reaction, reaching a maximum of 87%. Attached Figure Description
[0027] Figure 1 The image shows the X-ray diffraction pattern of the Fe2 / NC electrocatalyst prepared in the examples;
[0028] Figure 2 The elemental mapping diagram of C and Fe in the Fe2 / NC electrocatalyst prepared in Example 2 is shown below.
[0029] Figure 3 The image shows aberration-corrected annular dark-field phase scanning transmission electron microscope image of the Fe2 / NC electrocatalyst prepared in Example 2.
[0030] Figure 4 Transmission electron microscopy (TEM) image of the Fe2 / NC electrocatalyst prepared in Example 3;
[0031] Figure 5 This is a high-resolution transmission electron microscope image of the Fe2 / NC electrocatalyst prepared in Example 4;
[0032] Figure 6 The image shows the elemental mapping of C, N, and Fe in the Fe2 / NC electrocatalyst prepared in Example 4.
[0033] Figure 7 This is a transmission electron microscope (TEM) image of the Fe2 / NC electrocatalyst prepared in Example 5;
[0034] Figure 8 Transmission electron microscopy (TEM) image of the Fe2 / NC electrocatalyst prepared in Example 6;
[0035] Figure 9 The image shows the elemental mapping of C, N, and Al in the Al2 / NC electrocatalyst prepared in Example 8.
[0036] Figure 10 This is a spherical aberration corrected annular dark-field phase scanning transmission electron microscope image of the Al2 / NC electrocatalyst prepared in Example 8;
[0037] Figure 11 The X-ray diffraction pattern of the Al2 / NC electrocatalyst prepared in Example 9;
[0038] Figure 12 This is a high-resolution transmission electron microscope image of the Al2 / NC electrocatalyst prepared in Example 9;
[0039] Figure 13 The image shows aberration-corrected annular dark-field phase scanning transmission electron microscope image of the Fe1 / NC electrocatalyst prepared in Comparative Example 1.
[0040] Figure 14 The Fe2 / NC electrocatalysts prepared in Examples 4 and 7, the Fe1 / NC electrocatalysts prepared in Comparative Example 1, and the linear voltammetric curves of oxygen reduction in a commercial 20 wt% Pt / C electrolyte saturated with oxygen in 0.1 M KOH electrolyte are shown.
[0041] Figure 15 The linear voltammetric curves of the Fe2 / NC electrocatalyst prepared in Example 4 and commercial 20wt% Pt / C after 5000 potential cycles in oxygen-saturated 0.1 MKOH electrolyte are shown.
[0042] Figure 16 The H2O2 selectivity of the Al2 / NC electrocatalysts and the corresponding NC substrates prepared in Examples 8 and 9 in oxygen-saturated 0.1 MKOH electrolyte is shown. Detailed Implementation
[0043] The present invention will be further described below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in manuals, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified. The raw materials used in the following embodiments and comparative examples are all commercially available.
[0044] Example 1
[0045] A method for preparing a diatomic ferroelectric catalyst includes the following steps:
[0046] (1) The volatilization and adsorption process of ferric chloride dimer (Fe2Cl6):
[0047] Take 100 mg of nitrogen-doped carbon material (NC) and 10 mg of anhydrous FeCl3, and place them into two ceramic boats respectively. Then place the two ceramic boats in a tube furnace, and according to the direction of airflow in the tube furnace, place the ceramic boat containing anhydrous FeCl3 upstream and the ceramic boat containing NC downstream, with the two ceramic boats touching each other. Set the furnace temperature to 400℃ and hold for 3 hours. After naturally cooling to room temperature, collect the Fe2Cl6 / NC initial product from the ceramic boat that originally contained NC.
[0048] (2) Heat treatment process of Fe2Cl6 / NC primary product:
[0049] The Fe2Cl6 / NC primary product was placed in a tube furnace and heat-treated under an inert atmosphere. The furnace temperature was set to 700℃ and held for 1 hour. After natural cooling to room temperature, the diatomic ferroelectric catalyst, Fe2 / NC, was obtained.
[0050] Figure 1 The X-ray diffraction pattern of the Fe2 / NC electrocatalyst prepared in Example 1 shows that it contains only diffraction peaks of graphitized carbon and no diffraction peaks of iron species, indicating that Fe did not aggregate into large nanoparticles on the NC substrate.
[0051] Example 2
[0052] A method for preparing a diatomic ferroelectric catalyst includes the following steps:
[0053] (1) The volatilization and adsorption process of ferric chloride dimer (Fe2Cl6):
[0054] Take 50 mg of nitrogen-doped carbon material (NC) and 100 mg of anhydrous FeCl3, and place them into two ceramic boats respectively. Then place the two ceramic boats in a tube furnace, and according to the direction of airflow in the tube furnace, place the ceramic boat containing anhydrous FeCl3 in the upstream position and the ceramic boat containing NC in the downstream position, with the two ceramic boats touching each other. Set the furnace temperature to 400℃ and hold for 3 hours. After naturally cooling to room temperature, collect the Fe2Cl6 / NC initial product from the ceramic boat that originally contained NC.
[0055] (2) Heat treatment process of Fe2Cl6 / NC primary product:
[0056] The Fe2Cl6 / NC primary product was placed in a tube furnace and heat-treated under an inert atmosphere. The furnace temperature was set to 900℃ and held for 3 hours. After natural cooling to room temperature, the diatomic ferroelectric catalyst, Fe2 / NC, was obtained.
[0057] Figure 2 The figure shows the elemental mapping of C and Fe in the Fe2 / NC electrocatalyst prepared in Example 2. As can be seen from the figure, C and Fe elements are uniformly distributed on the NC substrate.
[0058] Figure 3 This is a spherical aberration-corrected annular dark-field scanning transmission electron microscope (STEM) image of the Fe2 / NC electrocatalyst prepared in Example 2. Pairs of iron atoms are marked with solid white circles (the brighter dots in circles A and B represent the superimposed projections of two iron atoms), totaling 21 pairs. The interatomic distances between the iron atoms are also indicated in nm. This indicates the presence of anchored iron diatoms on the substrate, with interatomic distances ranging from 0.19 to 0.32 nm. Single iron atoms are marked with dashed white circles, and statistically, iron diatoms account for as much as 72.4% of all atomic-level sites.
[0059] Example 3
[0060] A method for preparing a diatomic ferroelectric catalyst includes the following steps:
[0061] (1) The volatilization and adsorption process of ferric chloride dimer (Fe2Cl6):
[0062] Take 20 mg of nitrogen-doped carbon material (NC) and 100 mg of anhydrous FeCl3, and place them into two ceramic boats respectively. Then place the two ceramic boats in a tube furnace, and according to the direction of airflow in the tube furnace, place the ceramic boat containing anhydrous FeCl3 in the upstream position and the ceramic boat containing NC in the downstream position, with the two ceramic boats touching each other. Set the furnace temperature to 300℃ and hold for 1 hour. After naturally cooling to room temperature, collect the Fe2Cl6 / NC initial product from the ceramic boat that originally contained NC.
[0063] (2) Heat treatment process of Fe2Cl6 / NC primary product:
[0064] The Fe2Cl6 / NC primary product was placed in a tube furnace and heat-treated under a hydrogen atmosphere. The hydrogen volume concentration was set to 2%, the furnace temperature to 300℃, and the temperature was held for 1 hour. After natural cooling to room temperature, the diatomic ferroelectric catalyst, Fe2 / NC, was obtained.
[0065] Figure 1 The X-ray diffraction pattern of the Fe2 / NC electrocatalyst prepared in Example 3 shows that it contains only diffraction peaks of graphitized carbon and no diffraction peaks of iron species, indicating that Fe did not aggregate into large nanoparticles on the NC substrate.
[0066] Figure 4 The image shows a transmission electron microscope (TEM) image of the Fe2 / NC electrocatalyst prepared in Example 3. There are no obvious particles on the NC substrate, indicating that Fe is anchored on the NC substrate at the atomic scale.
[0067] Example 4
[0068] A method for preparing a diatomic ferroelectric catalyst includes the following steps:
[0069] (1) The volatilization and adsorption process of ferric chloride dimer (Fe2Cl6):
[0070] Take 50 mg of nitrogen-doped carbon material (NC) and 100 mg of anhydrous FeCl3, and place them into two ceramic boats respectively. Then place the two ceramic boats in a tube furnace, and according to the direction of airflow in the tube furnace, place the ceramic boat containing anhydrous FeCl3 in the upstream position and the ceramic boat containing NC in the downstream position, with the two ceramic boats touching each other. Set the furnace temperature to 400℃ and hold for 3 hours. After naturally cooling to room temperature, collect the Fe2Cl6 / NC initial product from the ceramic boat that originally contained NC.
[0071] (2) Heat treatment process of Fe2Cl6 / NC primary product:
[0072] The Fe2Cl6 / NC primary product was placed in a tube furnace and heat-treated under a hydrogen atmosphere. The hydrogen concentration was set to 5%, the furnace temperature to 400℃, and the temperature was held for 2 hours. After natural cooling to room temperature, the diatomic ferroelectric catalyst, Fe2 / NC, was obtained.
[0073] Figure 1 The X-ray diffraction pattern of the Fe2 / NC electrocatalyst prepared in Example 4 shows that it contains only diffraction peaks of graphitized carbon and no diffraction peaks of iron species, indicating that Fe did not aggregate into large nanoparticles on the NC substrate.
[0074] Figure 5The image shows a high-resolution transmission electron microscope (TEM) image of the Fe2 / NC electrocatalyst prepared in Example 4. The image shows no obvious particles or lattice on the NC substrate, indicating that Fe is anchored on the NC substrate at the atomic scale.
[0075] Figure 6 The figure shows the elemental mapping of C, N, and Fe in the Fe2 / NC electrocatalyst prepared in Example 4. As can be seen from the figure, C, N, and Fe elements are uniformly distributed on the NC substrate.
[0076] Example 5
[0077] A method for preparing a diatomic ferroelectric catalyst includes the following steps:
[0078] (1) The volatilization and adsorption process of ferric chloride dimer (Fe2Cl6):
[0079] Take 50 mg of nitrogen-doped carbon material (NC) and 100 mg of anhydrous FeCl3, and place them into two ceramic boats respectively. Then place the two ceramic boats in a tube furnace, and according to the direction of airflow in the tube furnace, place the ceramic boat containing anhydrous FeCl3 in the upstream position and the ceramic boat containing NC in the downstream position, with the two ceramic boats touching each other. Set the furnace temperature to 400℃ and hold for 3 hours. After naturally cooling to room temperature, collect the Fe2Cl6 / NC initial product from the ceramic boat that originally contained NC.
[0080] (2) Heat treatment process of Fe2Cl6 / NC primary product:
[0081] The Fe2Cl6 / NC primary product was placed in a tube furnace and heat-treated under a hydrogen atmosphere. The hydrogen concentration was set to 10%, the furnace temperature to 400℃, and the temperature was maintained for 2 hours. After natural cooling to room temperature, the diatomic ferroelectric catalyst, Fe2 / NC, was obtained.
[0082] Figure 1 The X-ray diffraction pattern of the Fe2 / NC electrocatalyst prepared in Example 5 shows that it contains only diffraction peaks of graphitized carbon and no diffraction peaks of iron species, indicating that Fe did not aggregate into large nanoparticles on the NC substrate.
[0083] Figure 7 The image shows a transmission electron microscope (TEM) image of the Fe2 / NC electrocatalyst prepared in Example 5. The image shows no obvious particles on the NC substrate, indicating that Fe is anchored on the NC substrate at the atomic scale.
[0084] Example 6
[0085] A method for preparing a diatomic ferroelectric catalyst includes the following steps:
[0086] (1) The volatilization and adsorption process of ferric chloride dimer (Fe2Cl6):
[0087] Take 50 mg of nitrogen-doped carbon material (NC) and 50 mg of anhydrous FeCl3, and place them into two ceramic boats respectively. Then place the two ceramic boats in a tube furnace, and according to the direction of airflow in the tube furnace, place the ceramic boat containing anhydrous FeCl3 in the upstream position and the ceramic boat containing NC in the downstream position, with the two ceramic boats touching each other. Set the furnace temperature to 500℃ and hold for 2 hours. After naturally cooling to room temperature, collect the Fe2Cl6 / NC initial product from the ceramic boat that originally contained NC.
[0088] (2) Heat treatment process of Fe2Cl6 / NC primary product:
[0089] The Fe2Cl6 / NC primary product was placed in a tube furnace and heat-treated under a hydrogen atmosphere. The hydrogen concentration was set to 5%, the furnace temperature to 600℃, and the temperature was maintained for 3 hours. After natural cooling to room temperature, the diatomic ferroelectric catalyst, Fe2 / NC, was obtained.
[0090] Figure 1 The image shows the X-ray diffraction pattern of the Fe2 / NC electrocatalyst prepared in Example 6. The pattern contains only diffraction peaks of graphitized carbon and no diffraction peaks of iron species, indicating that Fe did not aggregate into large nanoparticles on the NC substrate.
[0091] Figure 8 The image shows a transmission electron microscope (TEM) image of the Fe2 / NC electrocatalyst prepared in Example 6. The image shows no obvious particles on the NC substrate, indicating that Fe is anchored on the NC substrate at the atomic scale.
[0092] Example 7
[0093] A method for preparing a diatomic ferroelectric catalyst includes the following steps:
[0094] (1) The volatilization and adsorption process of ferric chloride dimer (Fe2Cl6):
[0095] Take 50 mg of nitrogen-doped carbon material (NC) and 100 mg of anhydrous FeCl3, and place them on carbon cloth and a porcelain boat, respectively. Place the carbon cloth with NC on the porcelain boat containing anhydrous FeCl3, and cover the carbon cloth with another porcelain boat. Then place the carbon cloth and porcelain boat in a muffle furnace. Set the furnace temperature to 400℃ and keep it at that temperature for 1 hour. After it cools naturally to room temperature, collect the Fe2Cl6 / NC primary product on the carbon cloth.
[0096] (2) Heat treatment process of Fe2Cl6 / NC primary product:
[0097] The Fe2Cl6 / NC primary product was placed in a tube furnace and heat-treated under an inert atmosphere. The furnace temperature was set to 900℃ and held for 2 hours. After natural cooling to room temperature, the diatomic ferroelectric catalyst, Fe2 / NC, was obtained.
[0098] Figure 1 The X-ray diffraction pattern of the Fe2 / NC electrocatalyst prepared in Example 7 shows that it contains only diffraction peaks of graphitized carbon and no diffraction peaks of iron species, indicating that Fe did not aggregate into large nanoparticles on the NC substrate.
[0099] Example 8
[0100] A method for preparing a diatomic aluminum electrocatalyst includes the following steps:
[0101] (1) The volatilization and adsorption process of aluminum chloride dimer (Al2Cl6):
[0102] Take 50 mg of nitrogen-doped carbon material (NC) and 100 mg of anhydrous AlCl3, and place them into two ceramic boats respectively. Then place the two ceramic boats in a tube furnace, and according to the direction of airflow in the tube furnace, place the ceramic boat containing anhydrous AlCl3 in the upstream position and the ceramic boat containing NC in the downstream position, with the two ceramic boats touching each other. Set the furnace temperature to 180℃ and hold for 2 hours. After naturally cooling to room temperature, collect the initial Al2Cl6 / NC product in the ceramic boat that originally contained NC.
[0103] (2) Heat treatment process of Al2Cl6 / NC primary product:
[0104] The initial product of Al2Cl6 / NC was placed in a tube furnace and heat-treated under a hydrogen atmosphere. The hydrogen concentration was set to 5%, the furnace temperature to 400℃, and the temperature was held for 2 hours. After natural cooling to room temperature, the diatomic aluminum electrocatalyst, namely Al2 / NC, was obtained.
[0105] Figure 9 The figure shows the elemental mapping of C, N, and Al in the Al2 / NC electrocatalyst prepared in Example 8. As can be seen from the figure, C, N, and Al elements are uniformly distributed on the NC substrate.
[0106] Figure 10 This is a spherical aberration-corrected annular dark-field scanning transmission electron microscope (STEM) image of the Al2 / NC electrocatalyst prepared in Example 8. Pairs of aluminum atoms are marked with solid white circles, totaling 12 pairs. The interatomic spacing of aluminum atoms is also indicated in nm. This demonstrates the presence of anchored aluminum diatoms on the substrate, with interatomic spacing ranging from 0.16 to 0.26 nm. Single aluminum atoms are marked with dashed white circles, and statistical analysis shows that aluminum diatoms account for as much as 75% of all atomic-level sites.
[0107] Example 9
[0108] A method for preparing a diatomic aluminum electrocatalyst includes the following steps:
[0109] (1) The volatilization and adsorption process of aluminum chloride dimer (Al2Cl6):
[0110] Take 50 mg of nitrogen-doped carbon material (NC) and 100 mg of anhydrous AlCl3, and place them into two ceramic boats respectively. Then place the two ceramic boats in a tube furnace, and according to the direction of airflow in the tube furnace, place the ceramic boat containing anhydrous AlCl3 in the upstream position and the ceramic boat containing NC in the downstream position, with the two ceramic boats touching each other. Set the furnace temperature to 300℃ and hold for 2 hours. After naturally cooling to room temperature, collect the initial Al2Cl6 / NC product in the ceramic boat that originally contained NC.
[0111] (2) Heat treatment process of Al2Cl6 / NC primary product:
[0112] The initial product of Al2Cl6 / NC was placed in a tube furnace and heat-treated under a hydrogen atmosphere. The hydrogen concentration was set to 5%, the furnace temperature to 400℃, and the temperature was held for 2 hours. After natural cooling to room temperature, the diatomic aluminum electrocatalyst, namely Al2 / NC, was obtained.
[0113] Figure 11 The image shows X-ray diffraction patterns of the Al2 / NC electrocatalyst prepared in Example 9 and the NC substrate. The Al2 / NC and NC have similar spectra, containing only diffraction peaks of graphitized carbon and no diffraction peaks of aluminum species, indicating that Al did not aggregate into large nanoparticles on the NC substrate.
[0114] Figure 12 The image shows a high-resolution transmission electron microscope (TEM) image of the Al2 / NC electrocatalyst prepared in Example 9. The image shows no obvious particles or lattice on the NC substrate, indicating that Al is anchored on the NC substrate at the atomic scale.
[0115] Comparative Example 1
[0116] The preparation method of single-atom ferroelectric catalysts adopts the traditional impregnation method, which includes the following steps:
[0117] 100 mg of nitrogen-doped carbon material (NC) was placed in 16 ml of deionized water and sonicated for 30 minutes to obtain a uniform NC dispersion. 9 mg of anhydrous FeCl3 was dissolved in 4 ml of deionized water to obtain a FeCl3 solution. The FeCl3 solution was added dropwise to the NC dispersion and stirred at room temperature for 12 h. After stirring, the obtained sample was washed several times with deionized water and anhydrous ethanol, and then placed in a 60°C oven to dry for 12 h. The dried sample was placed in a tube furnace and heat-treated in a hydrogen atmosphere according to step (2) of Example 4. The hydrogen concentration was set to 5%, the furnace temperature to 400°C, and the temperature was maintained for 2 h. After natural cooling to room temperature, a single-atom ferroelectric catalyst, Fe1 / NC, was obtained.
[0118] Figure 13 The image shows a spherical aberration-corrected annular dark-field scanning transmission electron microscope (STEM) image of the Fe1 / NC electrocatalyst prepared in Comparative Example 1. As can be seen from the image, iron exists in the Fe1 / NC electrocatalyst in the form of single iron atoms, which are marked with white circles.
[0119] Application Example 1
[0120] The electrochemical ORR (oxygen reduction) performance of the Fe2 / NC electrocatalysts prepared in Examples 4 and 7, the Fe1 / NC electrocatalyst prepared in Comparative Example 1, and the commercial 20wt% Pt / C catalyst was tested.
[0121] (1) Preparation of the working electrode:
[0122] Accurately weigh 5.0 mg of the catalyst to be tested, add 980 μL of ethanol and 20 μL of 5% Nafion solution (perfluorosulfonic acid polymer solution), and ultrasonically disperse for 2 h to obtain a catalyst dispersion. Then take 20 μL of the catalyst dispersion and drop it onto a disk electrode. After natural drying, the working electrode is obtained.
[0123] (2) Performance testing methods:
[0124] The electrochemical ORR assay employed a three-electrode reaction system, with a millstone rod as the counter electrode, a calomel electrode as the reference electrode, and a disc electrode coated with the catalyst to be tested as the working electrode. Cyclic voltammetry and linear voltammetry were performed in an oxygen-saturated 0.1 M KOH electrolyte.
[0125] Figure 14 The graphs show the ORR linear voltammetric curves of the Fe2 / NC electrocatalysts prepared in Examples 4 and 7, the Fe1 / NC electrocatalyst prepared in Comparative Example 1, and the commercial 20wt% Pt / C catalyst in oxygen-saturated 0.1M KOH electrolyte. The graphs show that the half-wave potentials of the Fe2 / NC electrocatalyst are 0.858 V vs. RHE and 0.887 V vs. RHE, respectively, which are significantly higher than the half-wave potential of the Fe1 / NC catalyst (0.831 V vs. RHE) and close to or higher than the half-wave potential of the commercial 20wt% Pt / C catalyst (0.871 V vs. RHE). This indicates that the prepared Fe2 / NC electrocatalyst has outstanding 4e... - ORR catalytic activity.
[0126] Figure 15The figure shows the ORR linear voltammetric curves of the Fe2 / NC electrocatalyst prepared in Example 4 and the commercial 20wt% Pt / C catalyst after 5000 potential cycles in an oxygen-saturated 0.1M KOH electrolyte. As can be seen from the figure, after 5000 potential cycles, the half-wave potential of the Fe2 / NC electrocatalyst decreased by only 5 mV, which is less than the 30 mV decrease in the half-wave potential of the commercial 20wt% Pt / C catalyst. This indicates that the prepared Fe2 / NC electrocatalyst has superior 4e... - ORR catalytic stability.
[0127] Application Example 2
[0128] The electrochemical ORR performance of the Al2 / NC electrocatalysts and the corresponding NC substrates prepared in Examples 8 and 9 was tested.
[0129] (1) Preparation of the working electrode:
[0130] Accurately weigh 5.0 mg of the catalyst to be tested, add 980 μL of ethanol and 20 μL of 5% Nafion solution (perfluorosulfonic acid polymer solution), and ultrasonically disperse for 2 h to obtain a catalyst dispersion. Then take 20 μL of the catalyst dispersion and drop it onto a ring-shaped electrode. After natural drying, the working electrode is obtained.
[0131] (2) Performance testing methods:
[0132] The electrochemical ORR assay employed a three-electrode reaction system, with a millstone rod as the counter electrode, a calomel electrode as the reference electrode, and a ring-disc electrode coated with the catalyst to be tested as the working electrode. Cyclic voltammetry and linear voltammetry were performed in an oxygen-saturated 0.1 M KOH electrolyte.
[0133] Figure 16 The figures show the H2O2 selectivity of the Al2 / NC electrocatalysts and the corresponding NC substrates prepared in Examples 8 and 9 in an oxygen-saturated 0.1 MkOH electrolyte. As can be seen from the figures, the H2O2 selectivity of the Al2 / NC electrocatalysts is between 73% and 87%, which is much higher than that of the NC substrate (below 50%). This indicates that the diatomic Al sites in the prepared Al2 / NC electrocatalysts possess catalytic 2e-ion activity. - The role of ORR, and it shows a prominent 2e - ORR selectivity.
Claims
1. A method for preparing a diatomic metal electrocatalyst, characterized in that, The diatomic metal electrocatalyst comprises: a conductive substrate, and a diatomic iron or diatomic aluminum supported on the conductive substrate, wherein the diatomic iron consists of two iron single atoms, the diatomic aluminum consists of two aluminum single atoms, and the distance between the two iron single atoms is less than or equal to 0.32 nanometers, and the distance between the two aluminum single atoms is less than or equal to 0.26 nanometers. The preparation method includes the following steps: (1) Select one of anhydrous ferric chloride and anhydrous aluminum chloride as the metal precursor, and place the metal precursor and the conductive substrate horizontally or vertically in the heating device, and the placement position is such that the volatilized metal chloride dimer vapor can contact the conductive substrate. The horizontal placement refers to the metal precursor being upstream and the conductive substrate being downstream; the vertical placement refers to the metal precursor being downstream and the conductive substrate being upstream. (2) Start the heating device described in step (1), heat treat the metal precursor and the conductive substrate at the first temperature, carry out the volatilization and adsorption process of the metal chloride dimer, and collect the conductive substrate that has adsorbed the metal chloride dimer after naturally cooling to room temperature. (3) The conductive substrate in step (2) that has adsorbed the metal chloride dimer is subjected to heat treatment under an inert or hydrogen atmosphere to obtain the diatomic metal electrocatalyst. The conductive substrate is a nitrogen-doped carbon material; In step (2), when the metal precursor is anhydrous ferric chloride, the first temperature is 300~500℃; when the metal precursor is anhydrous aluminum chloride, the first temperature is 180~300℃. In step (3), the inert atmosphere heat treatment is performed at a temperature of 700~900℃ for 1~3h; the hydrogen volume concentration in the hydrogen atmosphere heat treatment is 2~10%, the temperature is 300~600℃, and the time is 1~3h.
2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the metal precursor to the conductive substrate is 1:10 to 5:
1.
3. The preparation method according to claim 1, characterized in that, In step (2), the adsorption time is 1 to 3 hours.