Preparation method and application of supramolecular derived iron monatomic catalyst

Abstract

The preparation method comprises the following steps: chelating an iron source and an organic carbon source to form a complex, adding an organic nitrogen source and a zinc source serving as a space blocking agent, and enabling the complex to be combined with the organic nitrogen source through N-H... O hydrogen bonds and O-H... N hydrogen bonds, so as to obtain the supermolecule-derived iron monatomic catalyst. Forming a metal organic supramolecular precursor; and performing high-temperature pyrolysis on the metal organic supramolecular precursor to obtain the supramolecular derived iron monatomic catalyst. The preparation method disclosed by the invention is simple in process, short in time consumption, low in energy consumption, relatively low in cost and relatively high in safety, the prepared iron monatomic catalyst is applied to an electro-catalysis carbon dioxide reduction reaction, high-selectivity generation of carbon monoxide can be realized, and the catalyst shows good structural stability before and after the reaction.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and in particular relates to a preparation method and application of a supramolecular-derived iron single-atom catalyst. Background Art

[0002] The carbon dioxide reduction reaction (CO2RR) has emerged as a dual-functional solution, enabling carbon recycling and the sustainable synthesis of value-added chemicals. Among the numerous potential products, carbon monoxide (CO) is of particular interest as an important feedstock for various chemical processes, including the production of methanol, acetic acid, and hydrocarbons via Fischer-Tropsch synthesis.

[0003] Single-atom catalysts (SACs) with isolated active centers have attracted considerable attention due to their outstanding ability to suppress *H binding in competitive hydrogen evolution. Atom libraries have been employed as catalysts, ranging from main-group to transition metals. To enhance the efficiency of SAC-based CO₂RR to CO, numerous strategies have been proposed to improve weak *COOH adsorption with a single-line pathway (metal-C), focusing on the regulation of coordination number and atomic species.

[0004] SACs not only combine the dual advantages of heterogeneous catalysts and homogeneous catalysts, but also bridge the gap between the two through unique properties. SACs represent a paradigm shift in catalytic design, providing maximized metal utilization and tunable electronic structure. In single-atom catalysts, isolated metal atoms M coordinated with nitrogen (MNx) in carbon substrates exhibit excellent performance in electrocatalysis, providing a promising route for the electrocatalytic reduction of CO2. However, the construction of MNx sites remains a challenge because isolated active sites can easily aggregate into particles during the synthesis process, resulting in a loss of catalytic performance. As an alternative to noble metal catalysts, nitrogen-coordinated single metal active sites anchored in porous carbon (MNC) have recently been identified as a new class of efficient CO2RR catalysts. Due to their abundance, high conductivity and good durability, CO2 to CO conversion is possible in various MNC catalysts. However, due to the strong binding of *CO on a single Fe-Nx site, especially for concentrated electrolytes, the CO Faradaic efficiency (FE) is low. CO ) and partial current density (J CO) is not high, and Fe-NC exhibits a low CO formation potential. It is an important means to improve the CO2RR energy by adopting strategies such as changing the morphology and pore structure of the carbon substrate, adjusting the coordination structure and the local environment of the metal center. It is still challenging to design efficient iron-based catalysts for practical CO2RR applications. In the electrocatalytic reduction of carbon dioxide, achieving good current density, selectivity and durability is not an easy task. Moreover, as the cathode potential increases, it may be deactivated, and the high selectivity of carbon monoxide can only occur within a narrow window voltage. Therefore, it is very necessary to design an efficient iron-based catalyst for electrocatalytic carbon dioxide reduction. Summary of the Invention

[0005] Based on the problems existing in the above-mentioned prior art, the present invention provides a method for preparing a supramolecular-derived iron single-atom catalyst, aiming to enable the obtained iron-based material to achieve higher carbon monoxide selectivity, wider window voltage and better stability in the electrocatalytic reduction of carbon dioxide.

[0006] To achieve the purpose, the present invention adopts the following technical solutions:

[0007] A method for preparing a supramolecular derived iron single atom catalyst is characterized in that: first, an iron source and an organic carbon source are chelated to form a complex to achieve Fe 2+ Then, an organic nitrogen source and a zinc source as a space barrier are added to make the complex bind to the organic nitrogen source through NH…O hydrogen bonds and OH…N hydrogen bonds to achieve Fe 2+ The metal organic supramolecular precursor is then pyrolyzed at high temperature to obtain a supramolecular-derived iron single atom catalyst.

[0008] Step 1: dissolving an iron source and an organic carbon source in an organic solvent to obtain a complex solution; dissolving an organic nitrogen source and a zinc source in the same organic solvent to obtain a solution A; uniformly mixing the solution A and the complex solution, then pouring ultrapure water into the solution to obtain a mixed reaction liquid, and stirring the reaction at room temperature, accompanied by precipitation of a metal organic supramolecular precursor; after the reaction is completed, washing, centrifuging, and vacuum drying to obtain a metal organic supramolecular precursor;

[0009] Step 2: The metal organic supramolecular precursor obtained in step 1 is subjected to high temperature pyrolysis to obtain the supramolecular-derived iron single atom catalyst (denoted as Fe SAs-N / SC).

[0010] Furthermore, the iron source is ferrous chloride tetrahydrate, the organic carbon source is 2,2'-biquinoline-4,4'-dicarboxylic acid, the organic nitrogen source is melamine, and the zinc source is zinc nitrate hexahydrate.

[0011] Furthermore, the organic solvent is dimethyl sulfoxide (DMSO), and the volume ratio of the organic solvent to ultrapure water in the mixed reaction liquid is 1:1-2.

[0012] Furthermore, the molar ratio of the iron source, the organic carbon source, the melamine and the zinc source is 1:5-20:15-30:5-20.

[0013] Furthermore, the stirring reaction time at room temperature in step 1 is 1 to 4 hours.

[0014] Furthermore, in step 1: the washing centrifugation is performed multiple times of centrifugal washing using ultrapure water and anhydrous ethanol in sequence, and the centrifugal speed is 5000-20000 rpm; the vacuum drying temperature is 40-80° C. and the drying time is 10-20 h.

[0015] Furthermore, in step 2: the high-temperature pyrolysis is carried out under an inert atmosphere (one or more of nitrogen, argon, helium and neon), the pyrolysis temperature is 900-1100° C., and the time is 2-6 hours.

[0016] The supramolecularly derived iron single-atom catalyst prepared by the present invention is a carbon substrate with a hierarchical porous nitrogen-doped supramolecular structure on which iron single atoms are loaded. The catalyst can be used in electrocatalytic carbon dioxide reduction.

[0017] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0018] 1. This invention successfully prepared an Fe single-atom catalyst supported on a carbon substrate with a hierarchically porous, nitrogen-doped supramolecular structure through a cascade locking strategy. In this process, the Fe metal cation first chelates with the organic carbon source 2,2'-biquinoline-4,4'-dicarboxylic acid, effectively sequestering the Fe ion. It then binds to melamine via NH…O and OH…N hydrogen bonds to further isolate the metal complex. The resulting metal-organic supramolecular precursor is then pyrolyzed under an argon atmosphere to prepare Fe SAs-N / SC. Zinc nitrate, as a steric blocker, prevents Fe aggregation, thereby increasing the single-atom content and enabling complete volatilization under high-temperature pyrolysis conditions. This cascade locking method is highly simple and easily scalable, meeting the needs of large-scale production of single-atom materials and addressing a variety of potential applications. By optimizing performance through structural design, this invention provides an innovative strategy for designing efficient iron-based catalysts for practical CO2 reduction (CO2RR) applications. Therefore, this invention provides a solid path for high-performance electrocatalysts for CO2 reduction and various energy-related applications.

[0019] 2. The supramolecularly derived iron single-atom catalyst of the present invention is obtained by a room-temperature reaction, which has a simple process, short time consumption, low energy consumption, low cost, high safety, and can be mass-produced.

[0020] 3. The novel supramolecular-derived iron single-atom catalyst prepared by the present invention has high activity, high selectivity and a wide voltage window as a catalyst for the electrocatalytic reduction of carbon dioxide to carbon monoxide. In an H-type cell, the supramolecular-derived iron single-atom catalyst has a Faradaic efficiency (FE) of more than 90% for the reduction of CO2 to CO within a wide potential window of 250mV, and can reach up to 94% at -0.6V, far exceeding other iron-based comparison catalysts such as iron single-atom catalysts. This result shows that there are more active sites on Fe SAs-N / SC, thereby illustrating its excellent electrocatalytic CO2RR performance. In addition, in a constant potential test in an H-type cell, the Faradaic efficiency of the catalyst for the reduction of CO2 to CO remained basically above 90% within 15 hours, indicating that the catalyst has good stability. Therefore, the catalyst of the present invention has obvious cost advantages and excellent performance in electrocatalytic carbon dioxide reduction, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a scanning electron microscope image of the Fe SAs-N / SC catalyst prepared in Example 1.

[0022] Figure 2 This is a transmission electron micrograph of the Fe SAs-N / SC catalyst prepared in Example 1.

[0023] Figure 3 Dark field TEM image and elemental mapping of the Fe SAs-N / SC catalyst prepared in Example 1.

[0024] Figure 4 This is the X-ray diffraction spectrum of the Fe SAs-N / SC catalyst prepared in Example 1.

[0025] Figure 5 This is a 300 kV double spherical aberration corrected transmission electron microscope image of the Fe SAs-N / SC catalyst prepared in Example 1.

[0026] Figure 6 This is the linear sweep voltammetry (LSV) curve of the Fe SAs-N / SC catalyst prepared in Example 1 in an H-type cell.

[0027] Figure 7 This is the carbon monoxide Faraday efficiency diagram of the Fe SAs-N / SC catalyst prepared in Example 1 in an H-type cell.

[0028] Figure 8 This is a stability test diagram of the Fe SAs-N / SC catalyst prepared in Example 1 in an H-type cell.

[0029] Figure 9 This is the X-ray diffraction pattern of the Fe SAs-N / SC catalyst prepared in Example 1 after the stability test.

[0030] Figure 10 This is a transmission electron micrograph of the Fe SAs-N / SC catalyst prepared in Example 1 after the stability test.

[0031] Figure 11 This is the carbon monoxide Faraday efficiency diagram of the N / SC catalyst prepared in Comparative Example 1 in an H-type cell. DETAILED DESCRIPTION

[0032] To make the objectives, technical solutions, and advantages of the present invention more clear, the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0033] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0034] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0035] Example 1

[0036] This embodiment provides a method for preparing a supramolecularly derived iron single-atom catalyst, comprising the following steps:

[0037] Step 1: First, add 0.1 mmol of ferrous chloride tetrahydrate (FeCl2·4H2O) and 1 mmol of 2,2'-biquinoline-4,4'-dicarboxylic acid (BCA) to beaker A containing 50 mL of dimethyl sulfoxide (DMSO) and stir until dissolved. Simultaneously, add 2.5 mmol of melamine (BA) and 1 mmol of Zn(NO3)2·6H2O to beaker B containing 50 mL of DMSO and stir until dissolved. After the two beakers have dissolved, the solutions in the two beakers are combined and thoroughly stirred. Then, 100 mL of ultrapure water is quickly added to the clear solution and stirred for 2 hours, forming a yellow precipitate. After self-assembly, the precipitate is washed repeatedly with deionized water and ethanol and then dried in a vacuum oven at 60°C for 12 hours to obtain the metal-organic supramolecular precursor (denoted as ZnFe-BCA / MA).

[0038] Step 2: After the ZnFe-BCA / MA precursor is fully ground, it is placed in a tube furnace, heated to 950°C at a heating rate of 5°C / min in an argon flow, and thermally decomposed for 3 hours to obtain the Fe SAs-N / SC catalyst.

[0039] Figure 1 This is a scanning electron microscope image of the Fe SAs-N / SC catalyst prepared in Example 1. Figure 2 This is a transmission electron micrograph of the Fe SAs-N / SC catalyst prepared in Example 1. As can be seen from the figure, the Fe SAs-N / SC catalyst has a bow-tie-shaped structure formed by stacking a large number of nanosheets.

[0040] Figure 3 The dark field TEM image and element mapping of the Fe SAs-N / SC catalyst prepared in Example 1 show that the elements are evenly distributed.

[0041] Figure 4 This is the X-ray diffraction spectrum of the Fe SAs-N / SC catalyst prepared in Example 1. It can be seen that the Fe SAs-N / SC catalyst only exhibits two broad peaks centered at 26° and 44°, corresponding to the (002) and (101) planes of graphitic carbon, respectively. There are no diffraction peaks related to iron-based crystals, proving the absence of iron particles.

[0042] Figure 5 This is a 300 kV double spherical aberration corrected transmission electron micrograph of the Fe SAs-N / SC catalyst prepared in Example 1. It can be seen that single iron atoms are uniformly distributed in the Fe SAs-N / SC catalyst.

[0043] The Fe SAs-N / SC catalyst obtained in this example was tested for its CO2 reduction performance in an H-type cell. The catalyst was dispersed in a mixture of 10 μL of a 5 wt% Nafion solution and 0.99 mL of anhydrous ethanol. The mixture was ultrasonically dispersed for 30 minutes to prepare a catalyst ink. The resulting catalyst ink was loaded onto carbon paper (catalyst loading of 0.5 mg / cm2). 2 ), which was used as the working electrode of the three-electrode system, the platinum sheet was used as the counter electrode, and the silver chloride electrode filled with saturated potassium chloride solution was used as the reference electrode. The two electrolytic chambers were separated by an anion membrane. An H-type cell was assembled and the linear sweep voltammetry curve was tested in the H-type cell in a CO2-saturated electrolyte (0.5M KHCO3). The results are shown in Figure 2. Figure 6 The gas generated during the reduction process is collected with a vacuum air bag and analyzed by gas chromatography to analyze the Faraday efficiency of hydrogen and carbon monoxide. Figure 7 The Faraday efficiency of carbon monoxide in the H-type cell shows that the Faraday efficiency (FE) of CO2 reduction to CO exceeds 90% in the range of -0.75V to -0.5V (V vs. RHE) of the Fe SAs-N / SC catalyst, and reaches a maximum of 94% at -0.6V, with a voltage window of 250mV (FE CO >90%), showing excellent electrocatalytic CO2 reduction performance. This result indicates that Fe SAs-N / SC has a large number of active sites, thus explaining its excellent electrocatalytic CO2RR performance.

[0044] The H-type cell assembled with the supramolecular-derived iron single-atom catalyst was tested for the stability of carbon dioxide reduction using a constant potential test. Figure 8 This is a stability test of the Fe SAs-N / SC catalyst at -0.5 V (V vs. RHE). In this figure, the Faradaic efficiency of carbon monoxide of the Fe SAs-N / SC catalyst basically remains above 90% within 15 hours, indicating that the catalyst has good stability.

[0045] The catalyst was subjected to XRD and transmission characterization after 15 hours of reaction. The results are as follows: Figure 9 and Figure 10 As shown, it can be seen that the catalyst has good structural stability.

[0046] Comparative Example 1

[0047] In this comparative example, a comparative catalyst (named N / SC) was prepared in the same manner as in Example 1, except that the amount of ferrous chloride tetrahydrate added was 0.

[0048] The H-type cell carbon dioxide reduction performance test was performed on the N / SC catalyst obtained in this comparative example using the same method as in Example 1. The results are as follows: Figure 11 As shown in the figure, it can be seen that the Faradaic efficiency of N / SC to produce carbon monoxide by electrochemical reduction of carbon dioxide at -0.85V to -0.35V (V vs. RHE) is less than 90%, and the highest efficiency is only 50.1% at -0.5V. Compared with the Fe SAs-N / SC catalyst in carbon dioxide reduction, the performance is poor, indicating that in the competitive reaction of hydrogen evolution (HER) and carbon dioxide reduction reaction (CO2RR), the catalyst with the presence of single iron atoms has a better inhibitory effect on hydrogen evolution and better carbon dioxide reduction performance.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a supramolecularly derived iron single-atom catalyst, characterized in that: First, an iron source and an organic carbon source are chelated to form a complex, and then an organic nitrogen source and a zinc source as a steric blocker are added. The complex is combined with the organic nitrogen source through NH...O hydrogen bonds and OH...N hydrogen bonds to form a metal-organic supramolecular precursor. The metal-organic supramolecular precursor is then pyrolyzed at high temperature to obtain a supramolecular-derived iron single-atom catalyst.

2. The method for preparing the iron single-atom catalyst according to claim 1, wherein: The obtained iron single-atom catalyst is supported on a carbon substrate with a hierarchical porous nitrogen-doped supramolecular structure.

3. The method for preparing the supramolecularly derived iron single-atom catalyst according to claim 1, wherein: The following steps are involved: Step 1: dissolving an iron source and an organic carbon source in an organic solvent to obtain a complex solution; dissolving an organic nitrogen source and a zinc source in the same organic solvent to obtain a solution A; uniformly mixing the solution A and the complex solution, then pouring ultrapure water into the solution to obtain a mixed reaction liquid, stirring the mixture at room temperature to precipitate a metal organic supramolecular precursor; after the reaction is completed, washing, centrifuging, and vacuum drying the mixture to obtain a metal organic supramolecular precursor; Step 2: The metal organic supramolecular precursor obtained in step 1 is subjected to high temperature pyrolysis to obtain the supramolecular-derived iron single atom catalyst.

4. The method for preparing the supramolecularly derived iron single-atom catalyst according to claim 1, 2 or 3, characterized in that: The iron source is ferrous chloride tetrahydrate, the organic carbon source is 2,2'-biquinoline-4,4'-dicarboxylic acid, the organic nitrogen source is melamine, and the zinc source is zinc nitrate hexahydrate.

5. The method for preparing the supramolecularly derived iron single-atom catalyst according to claim 3, wherein: In step 1, the organic solvent is dimethyl sulfoxide, and the volume ratio of the organic solvent to ultrapure water in the mixed reaction liquid is 1:1-2.

6. The method for preparing the supramolecularly derived iron single-atom catalyst according to claim 1, 2 or 3, characterized in that: The molar ratio of the iron source, the organic carbon source, the organic nitrogen source and the zinc source is 1:5-20:15-30:5-20.

7. The method for preparing the supramolecularly derived iron single-atom catalyst according to claim 3, characterized in that: In step 1, the washing centrifugation is performed multiple times using ultrapure water and anhydrous ethanol in sequence, and the centrifugal speed is 5000-20000 rpm; the vacuum drying temperature is 40-80° C. and the drying time is 10-20 h.

8. The method for preparing the supramolecularly derived iron single-atom catalyst according to claim 3, wherein: In step 2, the high-temperature pyrolysis is carried out under an inert atmosphere, the pyrolysis temperature is 900-1100° C., and the time is 2-6 hours.

9. A supramolecularly derived iron single-atom catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the supramolecularly derived iron single-atom catalyst according to claim 9, characterized in that: As a catalyst for the electrocatalytic carbon dioxide reduction reaction.

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