Ionic liquid modified palladium-gold heterostructure electrocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrocatalysis CO2 reduction, and particularly relates to an ionic liquid modified palladium-gold heterostructure electrocatalyst and a preparation method and application thereof, and the ionic liquid modified palladium-gold heterostructure electrocatalyst comprises a Pd-Au heterostructure and an ionic liquid modified by the Pd-Au heterostructure; the Pd-Au heterostructure comprises a Pd nanometer sheet and Au nanometer particles loaded on the Pd nanometer sheet; the ionic liquid is one of 1-ethyl-3-methylimidazolium chloride and 1-butyl-1-methylpyrrolopyridine-bis (trifluoromethylsulfonyl) imide, and the ionic liquid is one of the following components: 1-ethyl-3-methylimidazolium chloride and 1-butyl-1-methylpyrrolopyridine-bis (trifluoromethylsulfonyl) imide. The ionic liquid is added into the electrocatalytic reaction, and the ionic liquid is used for modifying the CO2RR catalyst, so that the conductivity is improved, the concentration of CO2 adsorbed on the surface of the catalyst can be improved, and the aim of improving the CO2 reduction reaction activity and selectivity is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic CO2 reduction, and particularly relates to an ionic liquid-modified palladium-gold heterostructure electrocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] The excessive consumption of fossil energy has led to the release of a large amount of CO2, bringing a series of serious problems such as the greenhouse effect and seawater acidification. Carbon dioxide capture, artificial photosynthesis, and chemical fixation are considered effective means to reduce the content of carbon dioxide. Among these strategies, electrochemically reducing CO2 (CO2RR) to value-added products using renewable energy is a promising solution. And CO is one of the main components of syngas, which can be used as a raw material for the Fischer-Tropsch synthesis reaction and the alcohol synthesis reaction, and is an attractive product. Therefore, developing highly efficient and cost-effective electrocatalysts is of great significance for improving the electroreduction of CO2 to CO.

[0003] There are still certain challenges in the efficient progress of the CO2 reduction reaction: (1) The CO2 molecular structure is stable. The linear and stable structure of CO2 makes the processes of its adsorption on the catalytic site and subsequent carbon-oxygen bond cleavage difficult. Therefore, a relatively high energy is required to overcome the energy barrier for the chemical activation or reduction of CO2. (2) The solubility of CO2 in water is very low. Under the conditions of room temperature (25 °C) and standard atmospheric pressure (101 kPa), the solubility of CO2 molecules in neutral aqueous solution is about 0.034 mol·L -1 ; (3) The product selectivity is low. There are multiple products in the CO2 reduction reaction (such as CO, HCOOH, CH3OH, CH4, CH3COOH, C2H4, C2H5OH, etc.). The thermodynamic potentials between different product paths are not very different, resulting in low selectivity for specific reduction products. (4) Side reaction competition. The hydrogen evolution reaction (HER) occurs during the CO2 reduction reaction. Free protons undergo a reduction reaction on the cathode to generate H2. HER is more dominant at higher negative potentials, resulting in a decrease in the efficiency and selectivity of the electrocatalytic CO2 reduction reaction. To solve the above problems, developing highly efficient CO2 reduction electrocatalysts is the key to achieving efficient electrocatalytic CO2 reduction.

[0004] Noble metal catalysts (such as Au, Pd, and Ag, etc.) have different electronic configurations and can bind tightly to the *COOH intermediate, but it is difficult to bind to the generated *CO. Therefore, such metals tend to generate CO. Noble metal catalysts have become the focus of research on CO2RR. Single-metal catalysts have been deeply studied in the CO2 reduction reaction, but the performance and durability of these metals limit their wide application. Therefore, synthesizing multi-metal nanocatalysts can regulate the adsorption energy on the alloy surface through electronic effects and geometric structures to obtain higher selectivity for target products.

[0005] Ionic liquids (ILs) are usually composed of large organic cations and delocalized, structurally asymmetric anions. They have many excellent properties such as adjustable structure, low saturated vapor pressure, high thermal stability, high chemical stability, low volatility, and strong selectivity for CO2 absorption. Studies have found that ionic liquids exhibit good activity in the catalytic reduction of CO2. The introduction of ionic liquids provides a medium for the CO2 reduction process, enhances the CO2 absorption capacity, improves the selectivity of CO2 reduction, and inhibits the occurrence of hydrogen evolution reaction. There are two ways of its action: (1) Both the anions and cations of ionic liquids can affect the solubility of CO2, but the anions play a major role. However, by increasing the length of the alkyl chain on the imidazole ring, the solubility of CO2 in ionic liquids can also be appropriately increased. For example, about 0.0006 mol of CO2 gas can be dissolved in 1 mol of water. Yu et al. found that under the conditions of a pressure of 0.161 MPa and a temperature of 298 K, 1 mol of [EMIm][BF4] can dissolve 0.022 mol of CO2 gas. Muldoon et al. investigated the solubility of CO2 in various imidazole-based ionic liquids. (2) By introducing special functional groups such as amino, phenolic, and hydroxyl groups, the functionalization of ionic liquids is achieved, making them have specific chemical properties. The introduction of functional groups interacts with CO2 in a certain form, which will greatly enhance the stability, antioxidant capacity, and CO2 absorption and desorption performance of ionic liquids, and promote the reaction. For example: Luo et al. studied amino-functionalized ionic liquids and found that the dissolved CO2 forms intramolecular hydrogen bonds with the anions and cations of the ionic liquid. As the solubility of CO2 increases, the viscosity value of the ionic liquid does not increase significantly. Brennecke et al. designed an amino-functionalized ionic liquid for carbon capture, and each amino group can react with a free CO2 molecule to form a carbamic acid, achieving a high carbon capture effect.

[0006] Therefore, adding ionic liquids to the electrocatalytic reaction and modifying the CO2RR catalyst with ionic liquids can not only increase the conductivity but also provide the CO2 concentration adsorbed on the catalyst surface, achieving the purpose of improving the activity and selectivity of the CO2 reduction reaction. However, there are the following problems with ionic liquid-modified CO2RR catalysts: (1) High cost: Most ionic liquids are expensive. (2) Interface problem between ionic liquid and catalyst: The interfacial compatibility between ionic liquid and catalyst may be poor, resulting in the coverage or inactivation of active sites. (3) Mass transfer limitation: The high viscosity and low volatility of ionic liquids may lead to low mass transfer efficiency, thus affecting the catalytic performance. (4) Difficulty in design and optimization: Due to the diverse chemical properties of ionic liquids, their application in CO2RR requires precise structural characterization and performance testing, which poses higher requirements for the design and optimization of catalysts. Summary of the Invention

[0007] The object of the present invention is to provide an ionic liquid-modified palladium-gold heterostructure electrocatalyst, its preparation method and application, so as to overcome the deficiencies of the prior art, reasonably optimize the Pd-based catalyst, and prepare a molecular-functionalized heterostructure Pd-Au-IL electrocatalyst by the methods of epitaxial growth and stirring impregnation. Molecular-functionalized noble metal nanoparticles (NPs) are formed on Pd nanosheets (NSs), obtaining a large number of stable structures and exhibiting excellent CO2RR performance.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows:

[0009] In the first aspect, the present invention provides an ionic liquid-modified palladium-gold heterostructure electrocatalyst, which includes a Pd-Au heterostructure and an ionic liquid; the ionic liquid is modified on the surface of the Pd-Au heterostructure;

[0010] The Pd-Au heterostructure includes Pd nanosheets and Au nanoparticles supported on the Pd nanosheets;

[0011] The ionic liquid is one of imidazole-based, pyrrole-based and pyridine-based ionic liquids.

[0012] In some other embodiments, the ionic liquid is one of 1-ethyl-3-methylimidazolium chloride and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide;

[0013] The ionic liquid-modified palladium-gold heterostructure electrocatalyst has a three-dimensional structure;

[0014] The Pd nanosheets are oriented and grown along the (111) plane of Pd;

[0015] The average size of the Au nanoparticles is 4.5 - 5.0 nm.

[0016] In some other embodiments, the mass ratio of the Pd-Au heterostructure to the ionic liquid is 1:(1.2 - 1.5).

[0017] In the second aspect, the present invention provides a preparation method of the ionic liquid-modified palladium-gold heterostructure electrocatalyst described in the first aspect, including the following steps:

[0018] (1) Palladium acetylacetonate solution and hexacarbonylmolybdenum are added to dimethylformamide and reacted to obtain Pd nanosheets;

[0019] (2) The Pd nanosheets are dissolved in a solvent, and chloroauric acid is added, followed by hydrothermal reaction to prepare a Pd-Au heterostructure;

[0020] (3) Mix the Pd-Au heterostructure with an aqueous solution of ionic liquid, and then obtain the ionic liquid-modified palladium-gold heterostructure electrocatalyst after freeze-drying.

[0021] In some other embodiments, in step (1), the mass ratio of palladium acetylacetonate to molybdenum hexacarbonyl is 1:(1 - 1.2);

[0022] The ratio of molybdenum hexacarbonyl to dimethylformamide is (6 - 7) mg:1 mL;

[0023] The temperature of the reaction is 55 - 65 °C, and the time is 0.5 - 1 h;

[0024] The palladium acetylacetonate solution is a solution of palladium acetylacetonate, trioctylphosphine oxide, and n-octanoic acid;

[0025] The ratio of palladium acetylacetonate, trioctylphosphine oxide, and n-octanoic acid is (1 - 1.5) mg:(16 - 16.5) mg:1 mL;

[0026] After the reaction, it also includes centrifugation, washing, and freeze-drying treatments;

[0027] The rotation speed of the centrifugation is 6500 - 7500 rpm, and the centrifugation time is 1 - 5 min;

[0028] The washing is carried out with deionized water and ethanol respectively;

[0029] The temperature of the freeze-drying is -55 to -60 °C, and the time is 20 - 24 h.

[0030] In some other embodiments, in step (2), the mass ratio of the Pd nanosheets to chloroauric acid is 7:(1.0 - 1.5);

[0031] The ratio of the Pd nanosheets to the solvent is 1 mg:(5 - 6) mL;

[0032] The solvent is a mixed solvent of ethylene glycol and water;

[0033] Preferably, the mixing volume ratio of ethylene glycol and water in the solvent is 1:(1 - 3);

[0034] The temperature of the hydrothermal reaction is 175 - 185 °C, and the time is 1 - 3 h;

[0035] After the reaction, it also includes centrifugation, washing, and freeze-drying treatments.

[0036] In some other embodiments, in step (3), the mass ratio of the Pd-Au heterostructure to the ionic liquid is 1:(1.2 - 1.5);

[0037] The ionic liquid is one of 1-ethyl-3-methylimidazolium chloride and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide;

[0038] The temperature of the mixing is 55 - 65 °C, and the time is 4 - 6 h.

[0039] In a third aspect, the present invention provides the application of the ionic liquid-modified palladium-gold heterostructure electrocatalyst described in the first aspect in electrocatalytic carbon dioxide reduction.

[0040] In a fourth aspect, the present invention provides an electrocatalytic carbon dioxide electrode, comprising: an electrode body and the ionic liquid-modified palladium-gold heterostructure electrocatalyst described in the first aspect coated on the electrode body.

[0041] In a fifth aspect, the present invention provides a method for electrocatalytic carbon dioxide reduction, using the electrocatalytic carbon dioxide electrode described in the fourth aspect.

[0042] Advantages of the present invention:

[0043] (1) Optimize the Pd-based catalyst, and prepare a molecular-functionalized heterostructure Pd-Au-IL electrocatalyst by the methods of epitaxial growth and stirring impregnation. Molecular-functionalized noble metal nanoparticles (NPs) are formed on Pd nanosheets (NSs), obtaining a large number of stable structures and showing excellent CO2RR performance.

[0044] (2) Modifying the CO2RR catalyst with an ionic liquid can not only increase the conductivity, but also provide the concentration of CO2 adsorbed on the catalyst surface, achieving the purpose of improving the activity and selectivity of the CO2 reduction reaction. Description of the Drawings

[0045] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0046] Figure 1 For the present invention, the electron microscope images (SEM), transmission electron microscope images (TEM), high-resolution transmission electron microscope images (HRTEM) and elemental mapping images of Pd-Au-imidazolium and Pd-Au-imide in the embodiments are shown. Among them, (a) SEM image of Pd-Au-imidazolium, (b) TEM image of Pd-Au-imidazolium, (c) HRTEM of Pd-Au-imidazolium, (d) elemental mapping image of Pd-Au-imidazolium; (e) SEM image of Pd-Au-imide, (f) TEM image of Pd-Au-imide, (g) HRTEM of Pd-Au-imide, (h) elemental mapping image of Pd-Au-imide;

[0047] Figure 2 In the examples of the present invention, XRD, FT-IR spectra, and XPS spectra were used to characterize the fine structures of the prepared Pd NSs, Pd-Au, Pd-Au-imidazolium, and Pd-Au-imide. Among them, (a) XRD patterns of Pd NSs, Pd-Au, Pd-Au-imidazolium, and Pd-Au-imide; (b) FT-IR spectra of Pd NSs, Pd-Au, Pd-Au-imidazolium, and 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl); (c) FT-IR spectra of Pd NSs, Pd-Au, Pd-Au-imide, and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide; (d) Pd 3d XPS spectra of Pd NSs and Pd-Au; (e) Pd 3d XPS spectra of Pd NSs, Pd-Au, and Pd-Au-imidazolium; (e) Pd 3d XPS spectra of Pd NSs, Pd-Au, and Pd-Au-imide;

[0048] Figure 3 In the examples of the present invention, the test results of the CO2RR electrocatalytic performance of the catalyst are shown, where (a) is the LSV comparison diagram in a CO2-saturated 0.5 M KHCO3 solution, and (b) is the Faraday efficiency of the CO product. Detailed implementation methods

[0049] Those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Specific conditions are not specified in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. Components not specified by the manufacturer are all conventional products available commercially.

[0050] Example 1

[0051] 1 Synthesis of materials

[0052] (1) Synthesis of Pd nanosheets

[0053] 20 mg of Pd(acac)2 and 260 mg of TOPO were dissolved in 16 mL of n-octanoic acid and sonicated for 2 min to ensure complete dissolution and dispersion of the solute. Under a 60 °C water bath and an argon atmosphere, magnetic stirring was carried out for 30 min. Then, 20 mg of Mo(CO)6 and 3 mL of DMF were added; after continuous stirring for 1 h, it was observed that the color of the solution changed from light yellow to dark blue within 10 minutes, indicating the successful reduction of palladium ions. After the reaction continued for 1 h, the product was collected by centrifugation at 7000 rpm for 4 min. The product was washed with deionized water and ethanol multiple times and then freeze-dried to obtain Pd nanosheets, labeled as Pd NSs.

[0054] (2) Preparation of Pd-Au Heterostructure

[0055] The Pd-Au heterostructure material was prepared by a polyol reduction strategy: First, 7 mg of Pd nanosheets were dispersed in a mixed solution of 40 mL of ethylene glycol and water (volume ratio 1:1), and then 34.7 μL of 0.1 M HAuCl4·H2O was added. After 10 minutes of ultrasonic treatment to ensure uniform dispersion. Then, this glass bottle was placed in a 100 mL hydrothermal reactor and heated at 180 °C for 2 h to promote the formation of the Pd-Au heterostructure material. After the reaction, it was allowed to cool naturally to room temperature, and the product was collected by centrifugation and washed successively with deionized water and ethanol, and finally freeze-dried to obtain the Pd-Au heterostructure, labeled as Pd-Au.

[0056] (3) Preparation of Ionic Liquid Functionalized Pd-Au Heterostructure (Pd-Au-IL Heterostructure)

[0057] The Pd-Au-IL heterostructure material was prepared by a stirring impregnation strategy: 1-Ethyl-3-methylimidazolium chloride ([EMIM]Cl) and 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [BMPyrr][NTf2] were respectively added to water and ultrasonicated for 10 min to ensure uniform dispersion, obtaining [EMIM]Cl aqueous solution and [BMPyrr][NTf2] aqueous solution. Then the Pd-Au heterostructure was respectively added to the [EMIM]Cl aqueous solution and [BMPyrr][NTf2] aqueous solution, where the weight ratio of Pd-Au to ionic liquid ([EMIM]Cl, [BMPyrr][NTf2]) was 1:1.5, and the resulting mixture was continuously stirred at 60 °C for 5 h. After centrifugation, it was washed with deionized water and freeze-dried to obtain the [EMIM]Cl modified Pd-Au heterostructure and the [BMPyrr][NTf2] modified Pd-Au heterostructure, labeled as Pd-Au-imidazolium and Pd-Au-imide respectively.

[0058] It can be seen from the above preparation process that the concept adopted for the preparation of the Pd-Au-IL heterostructure material is:

[0059] First, Pd(acac)2 is reduced by CO decomposed from Mo(CO)6 in octanoic acid. The (111) plane of Pd has a specific crystal structure, and the strong adsorption effect on CO molecules leads to the oriented growth of Pd, finally forming ultrathin Pd nanosheets (PdNSs support). Then, by using the method of liquid-phase epitaxial growth, Au nanoparticles are successfully loaded on the Pd nanosheets, forming a Pd-Au heterostructure. Finally, 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [BMPyrr][NTf2] are modified on the Pd-Au catalyst by the method of stirring impregnation, and the finally prepared materials are Pd-Au-imidazolium and Pd-Au-imide.

[0060] Comparative Example 1

[0061] Different from Example 1, step (2) is omitted, that is, the Pd nanosheets prepared in step (1) are directly placed in the aqueous solutions of [EMIM]Cl and [BMPyrr][NTf2] respectively to prepare Pd nanosheets modified with [EMIM]Cl and [BMPyrr][NTf2] respectively, which are labeled as Pd-imidazolium and Pd-imide. Other preparation steps are the same as those in Example 1.

[0062] Comparative Example 2

[0063] Different from Example 1, the method in Example 1 of Patent Publication No. CN116239109A is used to prepare graphene oxide to replace the Pd nanosheets prepared in step (1), and other preparation steps are the same as those in Example 1.

[0064] Comparative Example 3

[0065] Different from Example 1, 4-mercaptobenzoic acid (4-MBA) and 4-carboxy-2-mercapto-5-pyrimidinecarboxylic acid are used to replace [EMIM]Cl and [BMPyrr][NTf2] in step (3) to modify the Pd-Au catalyst. Other preparation steps are the same as those in Example 1.

[0066] Comparative Example 4

[0067] Different from Example 1, 1-ethyl-3-methylimidazolium thiocyanate (EMIM SCN) is used to replace [EMIM]Cl in step (3) to modify the Pd-Au catalyst.

[0068] 2 Experimental Results and Discussion

[0069] (1) The morphology and microstructure of Pd-Au-imidazolium and Pd-Au-imide were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and elemental mapping. The results are as follows Figure 1 shown, where (a) SEM image of Pd-Au-imidazolium, (b) TEM image of Pd-Au-imidazolium, (c) HRTEM of Pd-Au-imidazolium, (d) elemental mapping of Pd-Au-imidazolium; (e) SEM image of Pd-Au-imide, (f) TEM image of Pd-Au-imide, (g) HRTEM of Pd-Au-imide, (h) elemental mapping of Pd-Au-imide.

[0070] From Figure 1 it can be seen that in the SEM image of Pd-Au-imidazolium ( Figure 1 a), no aggregation of Au particles was found, and the nanosheets still maintained a good morphology. In the TEM image ( Figure 1 b), it can be seen that smaller Au NPs with an average size of 4.9 nm were uniformly anchored on the Pd NSs. HRTEM showed that the lattice spacing of the Pd(111) plane was 0.226 nm, and the lattice spacing of the Au(111) plane was 0.232 nm ( Figure 1 c). In addition, EDS elemental mapping ( Figure 1 d) further showed that the characteristic elements Pd, Au and Cl of the imidazolium molecule were uniformly distributed on the Pd NSs. From Figure 1 e, it can be seen that the Pd-Au-IL nanosheets had a ribbon-like three-dimensional structure and a smooth surface, and no aggregation of metal particles was seen. Transmission electron microscopy (TEM) images showed ( Figure 1 f) that with the assistance of imide ionic liquid, the synthesized Pd-Au-imide was well controlled and showed a uniform shape with an average size of about 4.3 nm. From Figure 1 g, it can be proved that the characteristic lattice fringe spacing of Pd was 0.226 nm, and the characteristic lattice fringe spacing of Au was 0.236 nm. In addition, the EDS map ( Figure 1 h) proved that the characteristic elements Pd, Au and F of the imide molecule were uniformly distributed on the Pd NSs, proving that 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [BMPyrr][NTf2] were successfully introduced onto the Pd-Au heterostructure and were in a uniformly dispersed state.

[0071] (2) The fine structure characterizations of the prepared Pd NSs, Pd-Au, Pd-Au-imidazolium and Pd-Au-imide by XRD, FT-IR spectra and XPS spectra are as followsFigure 2 As shown, where (a) XRD patterns of Pd NSs, Pd-Au, Pd-Au-imidazolium, and Pd-Au-imide; (b) FT-IR spectra of Pd NSs, Pd-Au, Pd-Au-imidazolium, and 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl); (c) FT-IR spectra of Pd NSs, Pd-Au, Pd-Au-imide, and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide; (d) Pd 3d XPS spectra of Pd NSs and Pd-Au; (e) Pd 3d XPS spectra of Pd NSs, Pd-Au, and Pd-Au-imidazolium; (e) Pd 3d XPS spectra of Pd NSs, Pd-Au, and Pd-Au-imide.

[0072] As Figure 2 As shown in (a), in the XRD patterns of Pd NSs, Pd-Au, and Pd-Au-IL, no diffraction peaks corresponding to Au appeared. This is due to the low crystallinity of the ultrasmall Au nanoclusters. Moreover, when comparing the addition of different ILs, the positions of the XRD diffraction peaks are almost the same, indicating that the addition of IL does not affect the crystal structure of Pd-Au. Five strong peaks are located at about 2θ = 40.2°, 46.8°, 68.3°, 82.4°, and 86.9°, which well confirm the FCC structure of Pd [PDF#87-0638].

[0073] The surface functional groups and structures of Pd, Pd-Au, and Pd-Au-IL samples were further investigated by Fourier transform infrared (FT-IR) spectroscopy. It can be clearly seen from the FT-IR that many new absorption peaks appeared in the spectra of Pd-Au-IL samples compared with those of Pd-Au samples. After adding imidazolium molecules ( Figure 2 b), the peak appearing at 1172 cm -1 is the in-plane stretching vibration absorption peak of H-C-N on the imidazole ring. After adding trifluoromethylimide molecules ( Figure 2 c), the peak appearing at 1150 cm -1 is the stretching vibration of the CF3 group, and the peak appearing at 600 cm -1 is the bending vibration of the CF3 group. The existence of these absorption peaks was not observed in the spectra of Pd and Pd-Au samples, proving the successful addition of imidazolium and trifluoromethylimide molecules.

[0074] In addition, X-ray photoelectron spectroscopy (XPS) was used to further study the valence states of various elements on the surfaces of Pd NSs, Pd-Au, and Pd-Au-IL samples. The high-resolution Pd 3d XPS spectra of Pd NSs and Pd-Au are as Figure 2As shown in d. Compared with Pd NSs, the position of the Pd 3d diffraction peak in the Pd-Au sample shows an obvious negative shift of 0.5 eV. This result indicates that electron transfer occurs in the Pd-Au heterostructure, with electrons transferring from Au to Pd, thereby regulating the electronic structure of Pd and promoting the CO2RR performance. After adding the ionic liquid containing imidazolium ( Figure 2 e), the sample shows both Pd 2+ and Pd 0 characteristic spectral peaks. The spectral peaks in the spectrum corresponding to binding energies of 337.5 and 343.0 eV are the 3d 2+ and 3d 5 / 2 electron binding energies of Pd 3 / 2 respectively, and the binding energies at 334.9 and 340.0 eV correspond to the 3d 0 and 3d 5 / 2 electron binding energies of Pd 3 / 2 respectively. After adding the ionic liquid containing trifluoromethylimide ( Figure 2 f), the Pd-Au-imide sample shows a significant positive core-level shift of 0.8 eV, indicating electron transfer from the Pd-Au heterostructure to the molecule, thereby inducing more electrons at the active sites near the ligand atoms and promoting the formation of *COOH, thus improving the activity and Faraday efficiency of CO production.

[0075] (3) To characterize the electrochemical reduction performance of the catalytic material for CO2, the obtained ionic liquid-functionalized Pd-Au heterostructure catalyst material was prepared into a working electrode. Through an electrochemical workstation (CHI760E), a two-compartment three-electrode reaction system was built, with the electrocatalyst as the working electrode, Ag / AgCl electrode as the reference electrode, and graphite rod as the counter electrode. All carbon dioxide reduction electrocatalytic reactions were carried out in a sealed H-type electrolytic cell, and the cathode and anode chambers of the electrolytic cell were separated by a Nafion proton exchange membrane.

[0076] The catalyst was electrolyzed by the constant voltage method, and the products were collected for analysis. Since the products are only gases, a gas chromatograph (GC) was used to detect the gas-phase products. CO and H2 are the two main products of CO2 reduction in this system. The test results of the CO2RR electrocatalytic performance of Pd, Pd-Au, Pd-IL, and Pd-Au-IL catalysts are as Figure 3 shown, where (a) is the LSV comparison diagram in a 0.5 M KHCO3 solution saturated with CO2, and (b) is the Faraday efficiency of the CO product.

[0077] In a 0.5 M KHCO3 solution saturated with CO2, first, LSV was used to test the molecular-functionalized Pd-Au catalyst ( Figure 3a). In the voltage range of -0.2V to -1.0V vs. RHE, the onset potential of all catalysts is approximately -0.4V vs. RHE. After adding the functionalized ionic liquid, the current density of the catalyst increases, indicating its good electrocatalytic CO2 reduction activity. It can be clearly seen that the current density of Pd-Au-imidazolium is 13.3 mA cm -2 , and as the potential increases, the current density of all samples gradually increases with the increase of potential, among which the current density of Pd-Au-imidazolium always remains the largest.

[0078] Figure 3 b shows the Faraday efficiency of CO for all catalysts at different potentials. It is worth noting that compared with Pd and Pd-Au, the catalysts with functionalized ionic liquids always have higher CO selectivity in the entire test voltage range. Among them, the highest FE of Pd is 62.1% at -0.6V vs. RHE, while the FE of Pd-imidazolium and Pd-imide with molecular functionalization CO is 83% and 76.4% respectively at the same potential. Especially for Pd-Au-imidazolium and Pd-Au-imide catalysts, the Faraday efficiency of CO can reach about 98.5% and 96.5%. While Pd and Pd-Au catalysts produce a large amount of H2 at high potentials, and the Faraday efficiency of H2 is about 60%; Pd-Au-imidazolium and Pd-Au-imide catalysts have better CO production performance, and the Faraday efficiency of CO is higher than 80% at a wide range of potentials.

[0079] Table 1 shows the electrochemical reduction performance of Comparative Examples 1-4 for CO2 at -0.6V vs (RHE) potential

[0080]

[0081] As can be seen from Table 1, the performance of Comparative Examples 1-4 is lower than that of Example 1. The synthesis of Pd-Au heterostructures with epitaxial growth characteristics, the addition of Au can optimize the electron distribution through energy band adjustment and interface effects, thereby improving the catalytic performance. However, during long-term reactions, the Pd-Au heterostructure may undergo phase separation or interface degradation, resulting in performance degradation. The addition of 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [BMPyrr][NTf2] ionic liquids to this heterostructure leads to electron transfer, regulates the intrinsic activity, and at the same time improves the ability of the catalyst to adsorb CO2 and helps to stabilize the *CO2ˉ intermediate, promoting the progress of the CO2RR process, demonstrating a new idea and possibility to promote the CO2RR reaction through catalyst surface functionalization.

[0082] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An ionic liquid-modified palladium-gold heterostructure electrocatalyst, characterized in that, It includes a Pd-Au heterostructure and an ionic liquid; the ionic liquid is modified on the surface of the Pd-Au heterostructure; The Pd-Au heterostructure includes Pd nanosheets and Au nanoparticles supported on the Pd nanosheets; The ionic liquid is one of imidazolium-based, pyrrolyl-based, and pyridinium-based ionic liquids.

2. The ionic liquid-modified palladium-gold heterostructure electrocatalyst according to claim 1, wherein The ionic liquid is one of 1-ethyl-3-methylimidazolium chloride and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide; The ionic liquid-modified palladium-gold heterostructure electrocatalyst has a three-dimensional structure; The Pd nanosheets are grown directionally along the (111) plane of Pd; The average size of the Au nanoparticles is 4.5 - 5.0 nm.

3. The ionic liquid-modified palladium-gold heterostructure electrocatalyst according to claim 1, wherein The mass ratio of the Pd-Au heterostructure to the ionic liquid is 1:(1.2 - 1.5).

4. A method for preparing an ionic liquid-modified palladium-gold heterostructure electrocatalyst according to any one of claims 1-3, characterized in that, It includes the following steps: (1) Palladium acetylacetonate solution and molybdenum hexacarbonyl are added to dimethylformamide and reacted to obtain Pd nanosheets; (2) The Pd nanosheets are dissolved in a solvent, and chloroauric acid is added, followed by a hydrothermal reaction to prepare a Pd-Au heterostructure; (3) The Pd-Au heterostructure is mixed with an aqueous solution of the ionic liquid and then freeze-dried to obtain the ionic liquid-modified palladium-gold heterostructure electrocatalyst.

5. The preparation method of the ionic liquid modified palladium-gold heterostructure electrocatalyst according to claim 4, characterized in that, In step (1), the mass ratio of palladium acetylacetonate to molybdenum hexacarbonyl is 1:(1 - 1.2); The ratio of molybdenum hexacarbonyl to dimethylformamide is (6 - 7) mg:1 mL; The temperature of the reaction is 55 - 65 °C, and the time is 0.5 - 1 h; The palladium acetylacetonate solution is a solution of palladium acetylacetonate, trioctylphosphine oxide, and n-octanoic acid; The ratio of palladium acetylacetonate, trioctylphosphine oxide, and n-octanoic acid is (1 - 1.5) mg:(16 - 16.5) mg:1 mL; After the reaction, it also includes centrifugation, washing, and freeze-drying treatments; The rotation speed of the centrifugation is 6500 - 7500 rpm, and the centrifugation time is 1 - 5 min; The washing is carried out with deionized water and ethanol respectively; The temperature of the freeze-drying is -55 to -60 °C, and the time is 20 - 24 h.

6. The preparation method of the ionic liquid-modified palladium-gold heterostructure electrocatalyst according to claim 4, characterized in that, In step (2), the mass ratio of the Pd nanosheets to chloroauric acid is 7:(1.0 - 1.5); The ratio of the Pd nanosheets to the solvent is 1 mg:(5 - 6) mL; The solvent is a mixed solvent of ethylene glycol and water; Preferably, the volume ratio of ethylene glycol to water in the solvent is 1:(1 - 3); The temperature of the hydrothermal reaction is 175 - 185 °C, and the time is 1 - 3 h; After the reaction, it also includes centrifugation, washing, and freeze-drying treatments.

7. The preparation method of the ionic liquid-modified palladium-gold heterostructure electrocatalyst according to claim 4, characterized in that In step (3), the mass ratio of the Pd-Au heterostructure to the ionic liquid is 1:(1.2 - 1.5); The ionic liquid is one of 1-ethyl-3-methylimidazolium chloride and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide; The temperature of the mixing is 55 - 65 °C, and the time is 4 - 6 h.

8. Application of the ionic liquid-modified palladium-gold heterostructure electrocatalyst according to any one of claims 1 - 3 in electrocatalytic carbon dioxide reduction.

9. An electrocatalytic carbon dioxide electrode, characterized in that, It includes: The electrode body and the ionic liquid-modified palladium-gold heterostructure electrocatalyst according to any one of claims 1-3 coated on the electrode body.

10. A method for electrocatalytic reduction of carbon dioxide, characterized in that, The electrocatalytic carbon dioxide electrode according to claim 9 is used.

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