Hydrophobic carbon-based monatomic catalyst and preparation method thereof

Abstract

The invention discloses a hydrophobic carbon-based monatomic catalyst and a preparation method thereof. The hydrophobic carbon-based monatomic catalyst comprises a carbon skeleton of a core-shell structure, a metal monatomic active site fixed on the carbon skeleton by forming a coordinate bond with N on the carbon skeleton, and an alkyl chain grafted on the carbon skeleton through a covalent bond. The alkyl chain is grafted through the covalent bond, chemical stable regulation and control of the hydrophobicity of the carbon-based nickel monatomic catalyst are achieved, covalent bond modification avoids the defects of a physical method, long-term stability of hydrophobicity is ensured, and efficient hydrophobic modification is achieved on the premise that monatomic sites are not damaged; a stable three-phase interface is formed on the hydrophobic surface, physical enrichment of CO2 near the catalyst is promoted, mass transfer resistance is reduced, CO2 diffusion is further accelerated through the hollow structure of the carbon skeleton, and the mass transfer capacity is improved.

Description

Technical Field

[0001] This invention relates to a hydrophobic carbon-based single-atom catalyst, and also to a method for preparing the above-mentioned hydrophobic carbon-based single-atom catalyst. Background Technology

[0002] In recent years, carbon-based single-atom catalysts (MNCs, where M = Fe, Co, Ni, Cu, etc.) have shown great potential in the field of electrocatalytic carbon dioxide reduction (CO2RR) due to their unique electronic structure, near 100% atom utilization, and excellent catalytic activity. However, traditional MNC catalysts typically have hydrophilic surfaces, which limits CO2 mass transfer at the electrode / electrolyte interface. Because CO2 has low solubility in aqueous solution (~34 mM, 25 °C) and a slow diffusion rate, a thick hydration layer easily forms on the surface of hydrophilic catalysts, hindering the contact between CO2 molecules and active sites, thereby reducing catalytic efficiency. Furthermore, during electrocatalysis, H2O molecules are more likely to undergo competitive hydrogen evolution reaction (HER) on the surface of hydrophilic catalysts, further reducing the selectivity of CO2RR. Therefore, optimizing the CO2 mass transfer process by controlling the hydrophilicity / hydrophobicity of the catalyst surface has become a key issue in improving CO2RR performance.

[0003] Existing research primarily employs physical methods to construct exogenous hydrophobic layers. Common strategies include coating a carbon substrate with a mixture of catalyst and hydrophobic materials (such as hydrophobic graphite, perfluoropolymers, or alkyl thiols) to achieve localized control of the gas-liquid-solid three-phase interface. However, the introduction of hydrophobicity through non-covalent physical methods suffers from poor durability, masking of active sites, and increased system resistance, limiting their practical applications. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a hydrophobic carbon-based single-atom catalyst with high activity, high selectivity and excellent CO2 mass transfer capability. Another purpose of this invention is to provide a method for preparing the above-mentioned hydrophobic carbon-based single-atom catalyst.

[0005] Technical solution: The hydrophobic carbon-based single-atom catalyst of the present invention includes a core-shell structured carbon skeleton, a metal single-atom active site fixed on the carbon skeleton by forming a coordination bond with N on the carbon skeleton, and an alkyl chain grafted on the carbon skeleton by a covalent bond.

[0006] The preparation method of the above-mentioned hydrophobic carbon-based single-atom catalyst includes the following steps:

[0007] (1) Preparation of MF (melamine-formaldehyde resin) nanopolymer spheres;

[0008] (2) MF nanopolymer spheres were dispersed in Tris-HCl buffer solution and ultrasonically treated to ensure uniform dispersion. Then, dopamine hydrochloride was added and stirred for 24 h. Dopamine molecules underwent self-polymerization and coated the surface of MF nanopolymer spheres through non-covalent interactions. MF@PDA was obtained. The mass ratio of MF nanopolymer spheres to dopamine hydrochloride was 2:1 to 3. By coating MF with polydopamine, electrostatic adsorption of metal cations can be achieved on the one hand, and the adsorption capacity of metal cations can be increased by coordinating and chelating metal cations on the other hand.

[0009] (3) MF@PDA and nitrate were dispersed in deionized water and stirred at room temperature for 24 h to promote the coordination of metal cations with the amino groups on polydopamine; after the reaction was completed, the catalyst precursor MF@PDA-M was obtained; the mass ratio of MF@PDA to nitrate was 1:1; the amount of metal cation added affected the formation of monomolecular dispersion, and excessive addition would form metal elemental nanoparticles, resulting in a decrease in catalytic performance;

[0010] (4) MF@PDA-M was heated to 350℃ under the protection of an inert gas flow and held at this temperature for 3h; then, it was heated to 900℃ at the same heating rate and held for 2h; after it was naturally cooled to room temperature, the M single-atom catalyst M-N4 with a unique M-4N coordination structure was obtained.

[0011] (5) The M-N4 catalyst was dispersed in an organic solvent containing chlorosilane and ultrasonically dispersed at 25°C for 2 h; subsequently, the obtained product was centrifuged and washed three times with an organic solvent to obtain a hydrophobic modified catalyst, labeled as M-N4@C n , where n represents the number of carbon atoms in the carbon chain of the modified silane; after calcination and pyrolysis, the oxygen-containing functional groups on the carbon skeleton react with the chlorosilane, thereby branching the silane carbon links onto the carbon skeleton. When there are too many silane carbon links, the conductivity decreases and the catalytic performance is reduced.

[0012] In step (1), the particle size of the MF nanopolymer spheres is 40–160 nm. If the particle size of the MF nanopolymer spheres is too small, they will be too dense when forming a catalyst layer on carbon paper, which is not conducive to CO2 gas transport and results in low mass transfer efficiency. If the particle size of the MF nanopolymer spheres is too large, the specific surface area will be reduced, which will reduce the number of metal single-atom active sites loaded on their surface.

[0013] In step (2), the pH of the Tris-HCl buffer solution is 8.5; after the polymerization reaction is completed, the product is centrifuged at 8000 rpm and dried overnight in a drying oven at 60°C.

[0014] In step (3), the nitrate is one of nickel nitrate, copper nitrate, cobalt nitrate, iron nitrate, bismuth nitrate, silver nitrate or tin nitrate. After the reaction is completed, the product is centrifuged at 6000 rpm, washed three times with deionized water, and dried overnight in a drying oven at 60°C.

[0015] In step (4), the inert gas is argon or nitrogen; the inert gas flow rate is 80–100 mL / min. -1 The gas washing time is 0.5–1 hour. The inert gas flow rate has a significant impact on the formation of monomolecular dispersions; excessively high flow rates can lead to the formation of metal clusters or metal nanoparticles.

[0016] In step (4), the heating rate is 1℃ / min. -1 .

[0017] In step (5), the chlorosilane is one of ethyltrichlorosilane, propyltrichlorosilane, butyltrichlorosilane, hexyltrichlorosilane, pentyltrichlorosilane, octyltrichlorosilane, octadecyltrichlorosilane or dimethyldichlorosilane.

[0018] In step (5), the organic solvent is n-hexane or toluene; after washing, the sample is placed in a vacuum drying oven and dried overnight at 100°C.

[0019] This invention constructs a hydrophobic carbon-based nickel single-atom catalyst by covalently grafting alkyl chains, which can significantly improve the electroreduction performance of CO2. This is because the gas-liquid-solid three-phase interface formed by hydrophobic modification can effectively promote CO2 enrichment and mass transfer, and inhibit the competitive HER reaction. In addition, the hollow structure (due to the different shrinkage degrees of MF and PDA during high-temperature pyrolysis, a core-shell carbon skeleton is formed, and the cavity structure of the carbon skeleton can also facilitate CO2 enrichment) and the atomically dispersed M-N4 sites synergistically increase the electron cloud density at the reaction site, reduce the reaction energy barrier, thereby improving the reaction efficiency and enhancing the CO Faraday efficiency.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention achieves chemical stability control of the hydrophobicity of carbon-based nickel single-atom catalyst by grafting alkyl chains with covalent bonds, and the covalent bond modification avoids the defects of physical methods, ensuring the long-term stability of hydrophobicity, and achieving efficient hydrophobic modification without destroying single-atom sites; (2) The present invention can precisely control the hydrophobicity of the catalyst surface by adjusting the length of alkyl chains, promoting CO2 enrichment while the hydrophobic surface repels water molecules in the electrolyte, reducing the local proton concentration at the interface, and significantly inhibiting competitive HER; (3) The hydrophobic surface of the present invention forms a stable three-phase interface, promotes the physical enrichment of CO2 near the catalyst, reduces the mass transfer resistance, and the hollow structure of the carbon skeleton further accelerates CO2 diffusion and improves the mass transfer capacity. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the preparation process of the hydrophobic carbon-based Ni single-atom catalyst in Example 1;

[0022] Figure 2 These are TEM images of the carbon-based Ni single-atom catalyst in Example 1 at different magnifications.

[0023] Figure 3 Specific surface area and porosity analysis of the carbon-based Ni single-atom catalyst in Example 1;

[0024] Figure 4 This is a comparative test of underwater bubble adhesion of the catalyst in Example 1;

[0025] Figure 5 This is a water-flooding comparison test of the original and hydrophobic catalysts in Example 1;

[0026] Figure 6 This is a comparison of the Faraday efficiencies of hydrophilic and hydrophobic carbon-based single-atom catalysts CO and H2 in the H-type electrolytic cell in Example 1;

[0027] Figure 7 This is a comparison of the Faraday efficiencies of hydrophilic and hydrophobic carbon-based single-atom catalysts CO and H2 in the flow cell in Example 1;

[0028] Figure 8 The changes in total current density and CO Faradaic efficiency of the hydrophobic carbon-based single-atom catalyst in Example 1 during a 30-hour stability test are shown.

[0029] Figure 9 This is a SEM image of the Cu-N4@C3 catalyst prepared in Example 2. Detailed Implementation

[0030] Example 1

[0031] The preparation method of the ethylchlorosilane-modified hydrophobic carbon-based Ni single-atom catalyst of the present invention includes the following steps:

[0032] (1) Hard template synthesis: 4.8 g of F127 surfactant was dissolved in 80 mL of deionized water and stirred at 25 °C and 600 rpm for 10 min to obtain a homogeneous solution; 4.8 g of 1,3,5-trimethylbenzene was added to the solution and stirring was continued for 6 h to obtain mixed solution A; 3.02 g of melamine, 1.94 g of formaldehyde aqueous solution (37 wt.%) and 0.4 mL of NaOH solution (0.1 mol L) were added to the solution. -1Dispersed in 320 mL of deionized water, the mixture was stirred at 98 °C and 400 rpm for 30 min to obtain a light blue prepolymer MF solution (solution B). Solution A was slowly added dropwise to solution B and mixed thoroughly. After 2 h, 0.54 mL of concentrated HCl (37 wt.%) was added (the amount of HCl added was adjusted to make the particle size of the MF nanopolymer spheres 40–160 nm), and stirring was continued for 6 h to induce the formation of MF nanopolymer spheres. The product was collected by centrifugation at 11,000 rpm and washed three times with deionized water and ethanol. The resulting white sample was dried overnight in a vacuum drying oven at 60 °C.

[0033] (2) Preparation of catalyst precursor: 200 mg of MF nanopolymer spheres were dispersed in 100 mL of Tris-HCl buffer solution (pH 8.5) and sonicated for 30 min to ensure uniform dispersion. Subsequently, 100 mg of dopamine hydrochloride was added and stirred at 30 °C for 24 h. Dopamine molecules underwent self-polymerization and coated the surface of MF nanopolymer spheres through non-covalent interactions. After the reaction was completed, the product was centrifuged at 8000 rpm and dried overnight in a drying oven at 60 °C to obtain dark gray MF@PDA. 100 mg of MF@PDA and 100 mg of nickel nitrate hexahydrate were dispersed in 100 mL of deionized water and stirred at 25 °C for 24 h to promote Ni 2+ The ions coordinated with the amino group on polydopamine. After the reaction was completed, the product was centrifuged at 6000 rpm, washed three times with deionized water, and dried overnight in a drying oven at 60℃ to obtain the catalyst precursor MF@PDA-Ni.

[0034] (3) High-temperature pyrolysis: MF@PDA-Ni powder was placed in an open alumina crucible and then placed in a tube furnace. The furnace was first purged with gas for 1 hour, and then pyrolyzed at 100 mL / min. -1 Under the protection of an inert gas (nitrogen) stream, at 1℃.min -1 The furnace temperature was raised to 350℃ at a heating rate and held at this temperature for 3 hours; then, the temperature was raised to 900℃ at the same heating rate and held for 2 hours; after it was allowed to cool naturally to room temperature, the M single-atom catalyst Ni-N4 with a unique Ni-4N coordination structure was obtained.

[0035] (4) Hydrophobic modification: 100 mg of Ni-N4 catalyst powder was dispersed in 15 mL of n-hexane containing 0.5 mL of ethyltrichlorosilane and ultrasonically dispersed at 25 °C for 2 h. Subsequently, the obtained product was centrifuged and washed three times with organic solvent to obtain the hydrophobic modified catalyst, which was labeled as Ni-N4@C2. After washing, the sample was placed in a vacuum drying oven and dried overnight at 100 °C.

[0036] pass Figure 2The TEM characterization results clearly show that the Ni-N4@C2 catalyst exhibits excellent morphological characteristics and structural advantages. For example... Figure 2 As shown in Figure a, the catalyst particles exhibit a highly uniform monodisperse state, with a particle size distribution concentrated between 100 and 160 nm. High-magnification TEM images reveal distinct depressions on the particle surface, indicating a rich porous structure on the material surface, such as... Figure 2 As shown in b. By comparing the bright and dark field images and the edge features of the broken particles, it can be confirmed that the material has a typical hollow structure. The spherical aberration corrected TEM characterization results show that ( Figure 2 c) The Ni catalyst exhibits an atomically dispersed state on the carbon support surface. The images clearly show that isolated Ni single-atom sites are uniformly distributed on the support surface, and no obvious metal nanoparticles or clusters were observed.

[0037] like Figure 3 As shown, the nitrogen adsorption-desorption isotherm of the Ni-N4@C2 catalyst exhibits typical type IV characteristics, accompanied by a significant H3-type hysteresis loop, indicating that the material possesses a rich mesoporous structure. BET calculations reveal a catalyst specific surface area as high as 850.11 m². 2 g -1 The high specific surface area provides ample exposed area for active sites in the catalytic reaction. Pore distribution analysis shows that the sharp peaks at 0.9 nm and 1.1 nm correspond to the inherent microporous structure of the carbon material framework. These micropores significantly increase the specific surface area of ​​the material and provide a confinement effect for the catalytic reaction. The peak at 10 nm originates from the macroporous structure on the outer surface of the internal MF carbon spheres; this mesoporous scale facilitates the rapid transport of reactants. The broad peak at 40 nm reflects the packing pores between Ni-N4@C2 nanoparticles. This macroporous structure helps to construct a three-dimensionally interconnected mass transfer network. The synergistic effect of this hierarchical porous system provides the catalyst with a high specific surface area, rapid mass transfer channels, and overall structural stability.

[0038] Depend on Figure 4 It is evident that Ni-N4 and Ni-N4@C2 catalysts exhibit drastically different gas-solid interface behaviors in underwater environments. The Ni-N4 catalyst displays superhydrophobic properties, with CO2 bubbles forming spherical shapes on its surface and easily detaching. In contrast, the hydrophobic Ni-N4@C2 catalyst exhibits gas-philic properties, with CO2 bubbles rapidly spreading and forming a gas film on its surface.

[0039] like Figure 5As shown, the dispersion behavior of Ni-N4 and Ni-N4@C2 catalysts in water exhibits significant differences. The Ni-N4 catalyst shows rapid water absorption and sedimentation, completely settling to the bottom within 15 minutes; while Ni-N4@C2 remains stably suspended on the water surface for a long time. This comparative experiment intuitively confirms that C2 alkyl group modification can effectively enhance the hydrophobicity and interfacial stability of the catalyst.

[0040] like Figure 6 As shown, electrochemical tests revealed that in an H-type electrolyzer, the CO Faradaic efficiency (FECO) of both Ni-N4@C2 and Ni-N4 catalysts exhibited a volcano-like trend (low at both ends and high in the middle) with increasing applied voltage. The Ni-N4@C2 catalyst demonstrated excellent CO selectivity at -0.8V (vs. RHE), with an FECO as high as 96.6%, significantly better than the 78.0% of the Ni-N4 catalyst. More importantly, the Ni-N4@C2 catalyst showed a significant inhibitory effect on the hydrogen evolution reaction (HER), with its HER Faradaic efficiency at -1.0V (vs. RHE) being only 2.35%, far lower than the 38.3% of the Ni-N4 catalyst. These data fully demonstrate that C2 group modification not only improves the CO selectivity of the catalyst but also effectively suppresses the competing HER side reaction.

[0041] like Figure 7 As shown, the Ni-N4 catalyst exhibits poor CO selectivity at all test potentials. Particularly in the high potential region (< -0.9 V), its HER contribution rate rises sharply to 78.7%, mainly attributed to the combined effect of limited CO2 mass transfer and ample proton supply at high current densities. In contrast, the Ni-N4@C2 catalyst demonstrates excellent CO selectivity (>99%) throughout the entire potential window (CO Faradaic efficiency ≥99% in 0.1 M KHCO3 electrolyte, especially at -0.6 V vs. RHE), with an HER contribution rate consistently below 1%. This significant performance difference stems from the unique hollow structure and abundant three-phase interfaces of Ni-N4@C2, structural features that effectively promote continuous CO2 supply while suppressing the occurrence of HER side reactions.

[0042] like Figure 8 As shown, the Ni-N4@C2 catalyst exhibits excellent CO2 electroreduction stability in a 1.0 M KOH electrolyte system. During a 32-hour continuous electrolysis test at a constant potential of -0.8 V (vs. RHE), the catalyst consistently maintained a flux of 108.2 mA / cm². -2 The catalyst exhibits a stable current density with potential fluctuations of less than 10mV. More importantly, the catalyst's performance degradation is negligible throughout the entire test (current density degradation rate <3%), and the CO Faradaic efficiency remains consistently above 85%.

[0043] Example 2

[0044] The preparation method of the propylchlorosilane-modified hydrophobic carbon-based Cu single-atom catalyst of the present invention includes the following steps:

[0045] (1) Hard template synthesis: 4.8 g of F127 surfactant was dissolved in 80 mL of deionized water and stirred at 25 °C and 600 rpm for 10 min to obtain a homogeneous solution; 4.8 g of 1,3,5-trimethylbenzene was added to the solution and stirring was continued for 6 h to obtain mixed solution A; 3.02 g of melamine, 1.94 g of formaldehyde aqueous solution (37 wt.%) and 0.4 mL of NaOH solution (0.1 mol L) were added to the solution. -1 Dispersed in 320 mL of deionized water, stirred at 98 °C and 400 rpm for 30 min to obtain a light blue prepolymer MF solution (solution B); solution A was slowly added dropwise to solution B and mixed thoroughly; after 2 h, 0.54 mL of concentrated HCl (37 wt.%) was added and stirring was continued for 6 h to induce the formation of MF nanopolymer spheres; the product was collected by centrifugation at 11000 rpm and washed three times with deionized water and ethanol respectively. The resulting white sample was dried overnight in a vacuum drying oven at 60 °C.

[0046] (2) Preparation of catalyst precursor: 200 mg of MF nanopolymer spheres were dispersed in 100 mL of Tris-HCl buffer solution (pH 8.5) and sonicated for 30 min to ensure uniform dispersion; then, 100 mg of dopamine hydrochloride was added and stirred at 30 °C for 24 h. Dopamine molecules underwent self-polymerization and coated the surface of MF nanopolymer spheres through non-covalent interactions. After the reaction was completed, the product was centrifuged at 8000 rpm and dried overnight in a drying oven at 60 °C to obtain dark gray MF@PDA; 100 mg of MF@PDA and 100 mg of copper nitrate trihydrate were dispersed in 100 mL of deionized water and stirred at 25 °C for 24 h to promote Cu 2+ The ions coordinate with the amino group on polydopamine. After the reaction is complete, the product is separated by centrifugation at 6000 rpm, washed three times with deionized water, and dried overnight in a drying oven at 60℃ to obtain the catalyst precursor MF@PDA-Cu.

[0047] (3) High-temperature pyrolysis: MF@PDA-Cu powder was placed in an open alumina crucible and then placed in a tube furnace. The furnace was first purged with gas for 30 min, and then pyrolyzed at 80 mL / min. -1 Under the protection of an inert gas (argon) stream, at 1℃ min -1The furnace temperature was raised to 350℃ at a heating rate and held at this temperature for 3 hours; then, the temperature was raised to 900℃ at the same heating rate and held for 2 hours; after it was allowed to cool naturally to room temperature, the M single-atom catalyst Cu-N4 with a unique Cu-4N coordination structure was obtained.

[0048] (4) Hydrophobic modification: 100 mg of Cu-N4 catalyst powder was dispersed in 15 mL of n-hexane containing 0.5 mL of propyltrichlorosilane and ultrasonically dispersed at 25 °C for 2 h. Subsequently, the obtained product was centrifuged and washed three times with organic solvent to obtain the hydrophobic modified catalyst, which was labeled as Cu-N4@C3. After washing, the sample was placed in a vacuum drying oven and dried overnight at 100 °C.

[0049] from Figure 9 The SEM images clearly show that the Cu-N4@C3 catalyst prepared in Example 2 has a good monodisperse spherical morphology and exhibits obvious surface depression structure features. The catalyst particles have a uniform size distribution with an average particle size of 100±15 nm; each spherical particle surface has nanoscale regular pits. This unique depression structure not only significantly increases the specific surface area of ​​the catalyst (reaching 945 m² as measured by BET), but also... 2 .g -1 More importantly, it can provide abundant diffusion channels and active site exposure surfaces for reactant molecules.

[0050] Contact angle tests showed a significant difference in surface wettability between Cu-N4 and Cu-N4@C3 catalysts. The Cu-N4@C3 catalyst exhibited a static water contact angle of 125.4°, showing typical hydrophobic properties; while the Cu-N4 catalyst had a contact angle of only 43.1°, exhibiting obvious hydrophilicity.

[0051] Example 3

[0052] The preparation method of the hexylchlorosilane-modified hydrophobic carbon-based Co single-atom catalyst of the present invention includes the following steps:

[0053] (1) Hard template synthesis: 4.8 g of F127 surfactant was dissolved in 80 mL of deionized water and stirred at 25 °C and 600 rpm for 10 min to obtain a homogeneous solution; 4.8 g of 1,3,5-trimethylbenzene was added to the solution and stirring was continued for 6 h to obtain mixed solution A; 3.02 g of melamine, 1.94 g of formaldehyde aqueous solution (37 wt.%) and 0.4 mL of NaOH solution (0.1 mol L) were added to the solution. -1Dispersed in 320 mL of deionized water, stirred at 98 °C and 400 rpm for 30 min to obtain a light blue prepolymer MF solution (solution B); solution A was slowly added dropwise to solution B and mixed thoroughly; after 2 h, 0.54 mL of concentrated HCl (37 wt.%) was added and stirring was continued for 6 h to induce the formation of MF nanopolymer spheres; the product was collected by centrifugation at 11000 rpm and washed three times with deionized water and ethanol respectively. The resulting white sample was dried overnight in a vacuum drying oven at 60 °C.

[0054] (2) Preparation of catalyst precursor: 200 mg of MF nanopolymer spheres were dispersed in 100 mL of Tris-HCl buffer solution (pH 8.5) and sonicated for 30 min to ensure uniform dispersion; then, 100 mg of dopamine hydrochloride was added and stirred at 30 °C for 24 h. Dopamine molecules underwent self-polymerization and coated the surface of MF nanopolymer spheres through non-covalent interactions. After the reaction was completed, the product was centrifuged at 8000 rpm and dried overnight in a drying oven at 60 °C to obtain dark gray MF@PDA; 100 mg of MF@PDA and 100 mg of cobalt nitrate hexahydrate were dispersed in 100 mL of deionized water and stirred at 25 °C for 24 h to promote the reaction of Co 2+ The ions coordinated with the amino group on polydopamine. After the reaction was completed, the product was separated by centrifugation at 6000 rpm, washed three times with deionized water, and dried overnight in a drying oven at 60℃ to obtain the catalyst precursor MF@PDA-Co.

[0055] (3) High-temperature pyrolysis: MF@PDA-Co powder was placed in an open alumina crucible and then placed in a tube furnace. The furnace was first purged with gas for 30 min, and then pyrolyzed at 80 mL / min. -1 Under the protection of an inert gas (argon) stream, at 1℃ min -1 The furnace temperature was raised to 350℃ at a heating rate and held at this temperature for 3 hours; then, the temperature was raised to 900℃ at the same heating rate and held for 2 hours; after it was allowed to cool naturally to room temperature, the M single-atom catalyst Co-N4 with a unique Co-4N coordination structure was obtained.

[0056] (4) Hydrophobic modification: 100 mg of Co-N4 catalyst powder was dispersed in 15 mL of toluene containing 0.5 mL of hexyltrichlorosilane and ultrasonically dispersed at 25 °C for 2 h. Subsequently, the obtained product was centrifuged and washed three times with organic solvent to obtain the hydrophobic modified catalyst, which was labeled as Co-N4@C6. After washing, the sample was placed in a vacuum drying oven and dried overnight at 100 °C.

[0057] Contact angle tests showed a significant difference in surface wettability between Co-N4 and Co-N4@C6 catalysts. The Co-N4@C6 catalyst exhibited a static water contact angle of 138.4°, demonstrating typical hydrophobic properties; while the Co-N4 catalyst had a contact angle of only 43.1°, exhibiting obvious hydrophilicity.

[0058] Example 4

[0059] The preparation method of the ethylchlorosilane-modified hydrophobic carbon-based Fe single-atom catalyst of the present invention includes the following steps:

[0060] (1) Hard template synthesis: 4.8 g of F127 surfactant was dissolved in 80 mL of deionized water and stirred at 25 °C and 600 rpm for 10 min to obtain a homogeneous solution; 4.8 g of 1,3,5-trimethylbenzene was added to the solution and stirring was continued for 6 h to obtain mixed solution A; 3.02 g of melamine, 1.94 g of formaldehyde aqueous solution (37 wt.%) and 0.4 mL of NaOH solution (0.1 mol L) were added to the solution. -1 Dispersed in 320 mL of deionized water, stirred at 98 °C and 400 rpm for 30 min to obtain a light blue prepolymer MF solution (solution B); solution A was slowly added dropwise to solution B and mixed thoroughly; after 2 h, 0.54 mL of concentrated HCl (37 wt.%) was added and stirring was continued for 6 h to induce the formation of MF nanopolymer spheres; the product was collected by centrifugation at 11000 rpm and washed three times with deionized water and ethanol respectively. The resulting white sample was dried overnight in a vacuum drying oven at 60 °C.

[0061] (2) Preparation of catalyst precursor: 200 mg of MF nanopolymer spheres were dispersed in 100 mL of Tris-HCl buffer solution (pH 8.5) and sonicated for 30 min to ensure uniform dispersion; then, 100 mg of dopamine hydrochloride was added and stirred at 30 °C for 24 h. Dopamine molecules underwent self-polymerization and coated the surface of MF nanopolymer spheres through non-covalent interactions. After the reaction was completed, the product was centrifuged at 8000 rpm and dried overnight in a drying oven at 60 °C to obtain dark gray MF@PDA; 100 mg of MF@PDA and 100 mg of ferric nitrate nonahydrate were dispersed in 100 mL of deionized water and stirred at 25 °C for 24 h to promote Ni 2+ The ions coordinated with the amino group on polydopamine. After the reaction was completed, the product was centrifuged at 6000 rpm, washed three times with deionized water, and dried overnight in a drying oven at 60℃ to obtain the catalyst precursor MF@PDA-Ni.

[0062] (3) High-temperature pyrolysis: MF@PDA-Fe powder was placed in an open alumina crucible and then placed in a tube furnace. The furnace was first purged with gas for 1 hour, and then pyrolyzed at 100 mL / min. -1 Under the protection of an inert gas (argon) stream, at 1℃ min -1 The furnace temperature was raised to 350℃ at a heating rate and held at this temperature for 3 hours; then, the temperature was raised to 900℃ at the same heating rate and held for 2 hours; after it was allowed to cool naturally to room temperature, the M single-atom catalyst Fe-N4 with a unique Fe-4N coordination structure was obtained.

[0063] (4) Hydrophobic modification: 100 mg of Fe-N4 catalyst powder was dispersed in 15 mL of n-hexane containing 0.5 mL of ethyltrichlorosilane and ultrasonically dispersed at 25 °C for 2 h. Subsequently, the obtained product was centrifuged and washed three times with organic solvent to obtain the hydrophobic modified catalyst, which was labeled as Fe-N4@C2. After washing, the sample was placed in a vacuum drying oven and dried overnight at 100 °C.

[0064] The Faraday efficiency (FF) of the catalyst was evaluated by controlling the potential of the H-type electrolyzer. GC and NMR analyses showed that the catalyst produced only CO and H2. Within the voltage range of -0.8 to -1.0 V, the FLACO of the hydrophobically modified catalyst Fe-N4@C2 consistently exceeded 60.0%. Fe-N4@C2 exhibited high FLACO across the entire potential range, reaching 95.9% at -0.8 V. Furthermore, the HER (hydrothermal activity) of Fe-N4@C2 was significantly suppressed, with FEH2 at only 5.25% at -0.1 V. In contrast, the FLACO of Fe-N4 was highly dependent on the applied potential; it initially increased and then decreased with increasing potential, reaching a maximum of 75.0% at -0.8 V. With further increases in applied potential, the competing HER began to dominate. These results indicate that the hydrophobically modified Fe single-atom catalyst Fe-N4@C2 exhibits good product selectivity in the electrocatalytic reduction of CO2 to CO.

[0065] The product selectivity of the catalysts was systematically evaluated using a flow electrolyzer system at different operating potentials. For the Fe-N4 catalyst, the Faraday efficiency of its hydrogen evolution reaction (HER) showed a trend of first decreasing and then increasing as the applied voltage increased from -0.2V to -1.2V, approaching complete selectivity (100%) at -1.2V. In contrast, the hydrophobically modified Fe-N4@C2 catalyst exhibited significantly improved CO selectivity, remaining above 90% throughout the entire test potential range, reaching a peak efficiency of 99.8% at -0.6V. This result indicates that surface hydrophobication treatment effectively suppresses competitive hydrogen evolution reaction and significantly improves the selectivity of CO2 reduction. In the 40-h stability test, the FECO and partial current density of the Fe-N4@C2 catalyst showed only a slight decrease, maintaining more than 80% of their initial values.

[0066] All electrochemical tests in this invention were performed on a CHI-760E electrochemical workstation, using both an H-type electrolytic cell and a self-made flow electrolytic cell for electrochemical rate measurement. The H-type electrolytic cell is a hermetically sealed dual-chamber structure, with the two chambers separated by a Nafion-117 proton exchange membrane. A three-electrode system was employed: the working electrode was a 5 mm diameter glassy carbon rotating disk electrode (RDE), and the counter electrode was a platinum mesh (1 × 1 cm). 2 The reference electrode was an Ag / AgCl electrode saturated with KCl solution. The working electrode was prepared as follows: 5 mg of catalyst sample was mixed with 950 μL of ethanol and 50 μL of 5 wt.% Nafion solution, ultrasonicated for 30 minutes to form a uniform ink, then coated onto carbon paper and vacuum dried at 60 °C. The effective area of ​​the working electrode was 1 × 1 cm². 2 The catalyst loading is 1 mg cm -2 Each compartment of the electrolytic cell was injected with 55 mL of 0.1 M KHCO3 electrolyte (leaving a 60 mL gas chamber at the top). Before testing, high-purity CO2 was continuously purged for 30 minutes to completely remove air. After CO2 saturation, the electrolyte pH was approximately 6.8. Stirring was maintained throughout the electrolysis process. All potentials were calibrated to the reversible hydrogen electrode (RHE) using the following formula:

[0067] E RHE =E Ag / AgCl +0.1989 +0.0591 × pH

[0068] Linear sweep voltammetry (LSV) was performed in a 0.1 M KHCO3 aqueous solution saturated with CO2 or N2. Cyclic voltammetry (CV) was performed using a 0.1 M KHCO3 electrolyte saturated with N2, with a scan potential range of -0.60 V to -0.50 V (vs. Ag / AgCl) and scan rates of 5, 10, 15, 20, 30, 40, and 50 mV s. -1To minimize the effects of the Faraday process, the capacitive current density (Δj = j) at -0.55V (vs. Ag / AgCl) was plotted. a -j c j a and j c The electrochemical active area (ECSA) was calculated by the slope of the linear relationship curves between the anodic and cathode current densities and the scan rate. Electrochemical impedance spectroscopy (EIS) was performed in a CO2-saturated 0.1 MkHCO3 solution using an AC voltage with an amplitude of 5 mV, in a frequency range of 0.01 Hz to 100 kHz, and the tests were conducted under open-circuit voltage.

[0069] In a flow electrolyzer system, a supported catalyst (1 mg cm⁻¹) is used. -2 Gas diffusion electrode (GDE, effective area 1×1cm) 2 As the cathode, nickel foam (1×1cm) 2 A saturated KCl solution Ag / AgCl electrode was used as the counter electrode, and a Versogen PiperION A20-HCO3 anion exchange membrane was used as the diaphragm. The electrolyte was a 1.0 M KOH solution. During the test, the electrolyte was continuously circulated in the anode and cathode chambers at a flow rate of 10 sccm using a peristaltic pump, and CO2 was continuously introduced into the electrolytic cell at a flow rate of 20 sccm. Gaseous products were monitored by online gas chromatography. All tests were performed at ambient temperature and pressure. Gaseous product components were quantitatively analyzed using a Shanghai Kechuang GC7900 gas chromatograph equipped with a flame ionization detector (FID, for CO detection) and a thermal conductivity detector (TCD, for H2 detection), with ultra-high purity argon (99.999%) as the carrier gas. Potential liquid products were analyzed using a Bruker Avance 600 nuclear magnetic resonance spectrometer.

[0070] This invention is used for the efficient electrochemical reduction of CO2 to CO, and solves the problems of active site masking due to hydrophobic modification of traditional carbon-based single-atom catalysts, difficulty in controlling the chemical inertness of carbon material surface, and severe competition for HER reaction. The catalyst of this invention exhibits excellent catalytic activity, CO selectivity and long-term stability.

Claims

1. A hydrophobic carbon-based single-atom catalyst, characterized in that: It includes a core-shell carbon skeleton, as well as metal single-atom active sites fixed on the carbon skeleton by forming coordination bonds with N on the carbon skeleton, and alkyl chains grafted onto the carbon skeleton by covalent bonds.

2. The method for preparing the hydrophobic carbon-based single-atom catalyst according to claim 1, characterized in that, Includes the following steps: (1) Preparation of MF nanopolymer spheres; (2) MF nanopolymer spheres were dispersed in Tris-HCl buffer solution, and after ultrasonic treatment, dopamine hydrochloride was added to the solution. Dopamine molecules underwent self-polymerization and coated the surface of MF nanopolymer spheres through non-covalent interactions; MF@PDA was obtained; the mass ratio of MF nanopolymer spheres to dopamine hydrochloride was 2:1 to 3. (3) MF@PDA and nitrate are dispersed in deionized water, and the metal cation coordinates with the amino group on polydopamine; after the reaction is completed, the catalyst precursor MF@PDA-M is obtained; wherein the mass ratio of MF@PDA to nitrate is 1:

1. (4) Under the protection of an inert gas flow, MF@PDA-M is first heated to 300-350℃ and held for 2-3 hours; then, it is heated to 800-900℃ at the same heating rate and held for 1.5-2 hours to obtain the M single-atom catalyst M-N4 with M-4N coordination structure. (5) The M-N4 catalyst was dispersed in an organic solvent containing chlorosilane. After ultrasonic dispersion, the resulting product was centrifuged and washed with an organic solvent to obtain the hydrophobic modified catalyst M-N4@C n , where n represents the number of carbon atoms in the carbon chain of the silane.

3. The preparation method according to claim 2, characterized in that: In step (1), the particle size of the MF nanopolymer spheres is 40-160 nm.

4. The preparation method according to claim 2, characterized in that: In step (3), the nitrate is one of nickel nitrate, copper nitrate, cobalt nitrate, iron nitrate, bismuth nitrate, silver nitrate, or tin nitrate.

5. The preparation method according to claim 2, characterized in that: In step (4), the inert gas is argon or nitrogen.

6. The preparation method according to claim 5, characterized in that: The flow rate of the inert gas is 80–100 mL / min. -1 The gas washing time is 0.5 to 1 hour.

7. The preparation method according to claim 1, characterized in that: In step (4), the heating rate is 1–1.5 °C / min. -1 .

8. The preparation method according to claim 1, characterized in that: In step (5), the chlorosilane is one of ethyltrichlorosilane, propyltrichlorosilane, butyltrichlorosilane, hexyltrichlorosilane, pentyltrichlorosilane, octyltrichlorosilane, octadecyltrichlorosilane or dimethyldichlorosilane.

9. The preparation method according to claim 1, characterized in that: In step (5), the organic solvent is n-hexane or toluene.

10. The preparation method according to claim 1, characterized in that: In step (5), after washing, the sample is dried overnight at 100-120°C.

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