Preparation and application of silver-modified copper-based electrocatalyst

Abstract

The preparation and application of a silver-modified copper-based electrocatalyst belong to the technical field of electrocatalyst preparation. The preparation method employs a wet chemical co-reduction strategy, involving the one-step co-reduction of copper and silver salt precursors in the liquid phase, followed by washing and drying to obtain the final catalyst. The introduction of silver forms a uniform heterogeneous interface between copper and silver, modulating the electronic structure of the copper active sites through interfacial electronic coupling effects. This results in high selectivity and high reactivity for multi-carbon products in alkaline electrolytes, making it suitable as a catalyst for the electrocatalytic reduction of carbon dioxide to multi-carbon products in alkaline environments. This silver-modified copper-based catalyst exhibits high activity, high selectivity for multi-carbon products, and significant stability at high current densities, demonstrating broad development prospects.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic materials technology, and more specifically, to a copper-based catalyst for electrocatalytic carbon dioxide reduction (CO2RR), particularly a silver-modified catalyst capable of efficiently, selectively, and stably converting carbon dioxide into ethylene, ethanol, and other multi-carbon (C2RR) compounds. 2+ Composite nanocatalysts of the product, their simple preparation method and applications. Background Technology

[0002] Global climate change has become a severe challenge facing human society, primarily attributed to the sharp rise in atmospheric carbon dioxide (CO2) concentration caused by the excessive consumption of fossil fuels since the Industrial Revolution. Capturing and converting CO2, a major greenhouse gas, is not only a key measure to mitigate climate change but also an important technological approach to building a sustainable energy system. Electrocatalytic carbon dioxide reduction (CO2RR) technology, utilizing electricity generated from renewable energy sources (such as solar and wind power) under mild conditions, converts CO2 molecules into high-value-added chemicals and fuels, and is considered one of the most promising technologies for CO2 resource utilization.

[0003] Among the many products of CO2RR, ethylene (C2H4) and ethanol (C2H5OH) are polycarbonate compounds containing two or more carbon atoms. 2+ Copper (Cu)-based products, due to their high energy density and important industrial status as bulk chemicals, are the most attractive target products in this field. Among various known electrocatalysts, copper (Cu)-based materials, due to their unique d-band electronic structure, are currently the only ones proven to effectively catalyze C-C bond coupling, thereby generating a large amount of C. 2+ The product is a single-metal catalyst.

[0004] However, traditional single-metal copper catalysts still face significant obstacles in their industrial application. Firstly, their effect on C... 2+ The selectivity of the product (measured by Faraday efficiency, FE) is typically low, especially at the high current densities required for high yields, where selectivity drops sharply. Secondly, in aqueous electrolytes, the competitive hydrogen evolution reaction (HER) is unavoidable, consuming significant amounts of input electrical energy and reducing energy conversion efficiency. It also occupies active sites on the catalyst, further worsening the selectivity of CO2RR. Thirdly, copper-based catalysts are highly susceptible to dynamic surface reconstruction, particle agglomeration, or loss of active components during electrocatalysis, leading to rapid degradation of catalytic performance, poor stability, and an inability to meet the long catalyst lifetime requirements of industrial production.

[0005] To overcome the aforementioned bottlenecks, academia and industry have conducted extensive research. Among these efforts, constructing bimetallic or multimetallic catalysts by combining copper with other metals has proven to be an effective strategy. By introducing a second metal (such as gold, zinc, tin, palladium, etc.), synergistic effects between elements can be utilized to optimize catalytic performance through mechanisms such as electron density modulation, lattice strain engineering, and tandem catalysis. Silver (Ag), as a relatively low-cost noble metal, exhibits high activity in the formation of carbon monoxide (CO) intermediates in CO2RR. Therefore, constructing a copper-silver (Cu-Ag) bimetallic system, utilizing Ag to efficiently generate CO, and then coupling CO via C-C at adjacent Cu sites to form the so-called "tandem catalysis" effect, is a promising approach to enhancing CO production. 2+ Selectivity is an important research direction.

[0006] Despite this, existing Cu-Ag catalysts still suffer from several shortcomings in preparation and performance. Many preparation methods, such as physical vapor deposition, magnetron sputtering, and electrodeposition, involve complex processes, require expensive vacuum equipment, and struggle to achieve uniform mixing of the two metals at the nanoscale and the construction of rich interfaces, thus limiting the full realization of synergistic effects. Simpler chemical methods, such as impregnation-reduction, often lead to severe metal particle agglomeration and insufficient exposure of active sites. Regarding performance, while existing Cu-Ag catalysts may offer improvements in certain aspects, few reports demonstrate the ability to simultaneously achieve the desired high C content in a single system. 2+ Selectivity (>80%), high yield (total current density >300 mA cm⁻¹) -2 The synergistic unity of three major objectives: strong inhibition of hydrogen evolution side reactions (HER FE < 15%).

[0007] Therefore, there is an urgent need in this field for a Cu-Ag bimetallic catalyst that is simple to prepare, low in cost, easy to scale up, and capable of producing a structure with controllable structure, excellent performance, and high stability, so as to promote the practical application of electrocatalytic CO2 reduction technology. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a silver-modified, highly efficient electrocatalyst for the reduction of carbon dioxide from copper-based substrates, its preparation method, and its applications. This method is simple, yields a unique catalyst structure, and can synergistically achieve the reduction of carbon dioxide at industrial-grade high current densities. 2+ The product exhibits high selectivity, high activity, and strong inhibition of the hydrogen evolution reaction, along with excellent long-term operational stability.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] The first aspect of the present invention provides a method for preparing a silver-modified copper-based electrocatalyst, comprising the following steps: (1) adding NaOH aqueous solution to CuCl2 solution to allow it to react fully; the molar ratio of CuCl2 to NaOH is 1:(30-5);

[0011] (2) After the reaction is complete, the resulting system is transferred to a water bath and hydrazine hydrate is slowly added. After the reaction, the system is cooled to room temperature. The molar ratio of CuCl2 to hydrazine hydrate is 1:(15-30).

[0012] (3) Add a solution containing AgNO3 to the cooled reaction system. The molar ratio of Cu to Ag is (5-20):1.

[0013] (4) Then, a reducing agent, ascorbic acid or NaBH4, was added to the above system. The solid product obtained after the reaction was washed, filtered and dried under vacuum to obtain the target silver-modified copper-based electrocatalyst.

[0014] The molar ratio of CuCl2 to reducing agent is 1:(0.2-0.8).

[0015] Furthermore, the molar ratio of copper to silver is 10:1.

[0016] Furthermore, the reduction reaction is carried out in a water bath at 60 °C.

[0017] Furthermore, it was prepared using the method described above.

[0018] Furthermore, the electrocatalyst is used in a gas diffusion electrode device to electrocatalyze the reduction of carbon dioxide to generate multi-carbon products.

[0019] Furthermore, the multi-carbon product includes ethylene and ethanol. The specific preparation method described above is as follows:

[0020] (1) At room temperature, CuCl2·2H2O (170.48 mg, 1 mmol) was dissolved in water (10 mL), and NaOH aqueous solution (1 M, 40 mL) was added under stirring to form a reaction system and allow it to react completely;

[0021] (2) Transfer the reaction system obtained in step (1) to a water bath at 60 °C, slowly add hydrazine hydrate (1 mL) under continuous stirring, and react for 1 h. After the reaction is completed, cool to room temperature.

[0022] (3) Add 10 mL of aqueous solution containing AgNO3 (8.49 mg, 0.05 mmol) to the system obtained in step (2) and stir rapidly for 30 min to initiate the reaction and form a solid product, wherein the molar ratio of Cu to Ag is 20:1; by adjusting the feeding ratio of Cu to Ag, catalysts with different compositions can be prepared.

[0023] (4) Separate the mixture containing solid products obtained in step (3), and wash, filter and vacuum dry the obtained solid in sequence to obtain silver-modified copper-based electrocatalyst.

[0024] In the above preparation method, as a preferred embodiment, the molar ratio of copper to silver in step (3) is in the range of (5:1) to (20:1). Through extensive experimental screening, it was found that when this molar ratio deviates from this range, the overall performance of the obtained catalyst will decrease.

[0025] In the above preparation method, as a more preferred embodiment, the molar ratio of copper to silver is 10:1. The catalyst prepared at this ratio exhibits the best catalytic activity and C... 2+ Selectivity and stability.

[0026] A second aspect of this invention provides a silver-modified copper-based electrocatalyst, which is prepared using the aforementioned method. This catalyst possesses the following unique structural and physicochemical properties:

[0027] The catalyst is composed of nanoparticles, with copper and silver elements uniformly distributed at the nanoscale, forming abundant copper-silver heterointerfaces. X-ray photoelectron spectroscopy characterization revealed that the Cu 2p... 3 / 2 The binding energy of silver exhibits a negative shift relative to that of pure copper, and the Ag 3d energy of silver is... 5 / 2 The binding energy is positively shifted relative to pure silver, indicating an electron transfer from silver to copper. Characterization by high-resolution transmission electron microscopy revealed that the (111) interplanar spacing of copper in the catalyst is expanded relative to the (111) interplanar spacing of pure copper, indicating tensile lattice strain.

[0028] Specifically:

[0029] Microstructure and elemental distribution: The catalyst is composed of nano-sized particles aggregated into an open packing structure with abundant pores. Elemental distribution analysis by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDS) revealed that copper and silver elements exhibit highly uniform distribution at both the individual particle and overall catalyst aggregate scales, without significant phase separation or large-sized single metal clusters. This indicates the formation of numerous and uniform copper-silver heterointerfaces at the nanoscale.

[0030] Electronic structure: X-ray photoelectron spectroscopy (XPS) analysis of the catalyst's surface chemical states revealed that, compared to reference standards of pure copper and pure silver, the Cu 2p group of copper in this catalyst was significantly larger. 3 / 2 The binding energy of the orbitals exhibits a negative shift (redshift) of approximately -0.11 eV, while the Ag 3d orbital energy of silver... 5 / 2 The binding energy of the orbitals shows a positive shift of approximately +0.17 eV (blue shift). This phenomenon is direct evidence of intermetallic charge transfer, clearly indicating that an electron transfer occurred from silver atoms to copper atoms at the Cu-Ag interface, resulting in a relatively electron-rich copper site at the interface.

[0031] Crystal Structure: Analysis of the catalyst's crystal structure using high-resolution transmission electron microscopy (HR-TEM) revealed clear lattice fringes belonging to both the (111) crystal planes of face-centered cubic (fcc) copper and silver. Precise measurements showed a significant expansion in the (111) interplanar spacing of copper in the catalyst (e.g., approximately 0.212 nm in the Cu:Ag=10:1 sample) compared to that of pure copper (approximately 0.209 nm). This lattice expansion is attributed to the tensile lattice strain introduced by the interaction of the larger silver atoms (~144 pm) with the smaller copper atoms (~128 pm) lattice.

[0032] The third aspect of this invention provides the application of the above-mentioned silver-modified copper-based electrocatalyst in the field of electrocatalytic carbon dioxide reduction.

[0033] Specifically, the application involves using this catalyst as a cathode catalyst in a gas diffusion electrode (GDE) flow cell reactor to electrocatalyze the reduction of carbon dioxide to multicarbons (C). 2+ )product.

[0034] As a preferred application method, the C 2+ The main products include ethylene and ethanol, both of which are chemicals of great industrial value.

[0035] As a preferred application method, this catalyst exhibits superior performance under industrially relevant operating conditions. Specifically, using an alkaline solution of 1 M KOH or similar concentration as the electrolyte, and applying a cathode potential no less than -1.0 V vs. RHE (reversible hydrogen electrode), the total current density is not less than -300 mA cm⁻¹. -2 Under these conditions, the catalyst catalyzes the reduction of carbon dioxide to C 2+ The overall Faraday efficiency of the product is not less than 80%, while the Faraday efficiency of the competing hydrogen evolution reaction is successfully suppressed to a level not higher than 15%.

[0036] Compared with the prior art, the present invention has the following significant advantages:

[0037] The preparation method is simple, green and low cost: The wet chemical reduction strategy adopted in this invention is carried out in an aqueous environment, without the need for high-temperature calcination or expensive vacuum equipment. The reaction conditions are easy to control and the raw materials are readily available, which greatly reduces the preparation cost of the catalyst and the environmental footprint, and has great potential for industrial scale-up.

[0038] Achieving a synergistic breakthrough in catalytic performance: The catalysts prepared in this invention, especially the sample with a Cu:Ag molar ratio of 10:1, have for the first time achieved synergistic high activity and high C content in a single system. 2+ Selective and strong HER inhibition. In this mechanism, Ag and Cu sites play different but complementary roles: Ag sites... The intermediate has weak adsorption, which allows it to efficiently reduce CO2 to... and promote Rapid desorption provides ample space for adjacent Cu sites. "Raw materials"; while Cu sites pair It has a moderate adsorption strength, which is beneficial for capturing the migrating organisms. And facilitates the key C-coupling steps, ultimately generating C 2+ Products. This functional division of labor and spatial synergy effectively overcomes the limitations of a single Cu catalyst. The dilemma of balancing generation and CC coupling. Simultaneously, it is speculated... Moderate coverage of intermediates will reduce The binding sites are targeted to inhibit hydrogen evolution. Specifically, this is achieved at binding sites exceeding -300 mA cm⁻¹. -2 Under high current density, C 2+ With a total Faraday efficiency of up to 80.87%, this performance index far exceeds that of most reported copper-based catalysts. At the same time, it reduces the energy loss of the hydrogen evolution side reaction to an extremely low level (~10%), greatly improving the overall efficiency and economy of electrocatalytic CO2 conversion.

[0039] Highly stable structure and long lifespan: The catalyst prepared by the method of this invention exhibits excellent anti-agglomeration and anti-reconfiguration capabilities due to its unique nanostructure and uniform elemental distribution. After long-term, high-current-density continuous electrolysis testing, the catalyst's microstructure, crystal structure, and chemical valence state remain highly stable, with no significant performance degradation observed, demonstrating excellent operational stability and meeting the stringent requirements of industrial applications for long catalyst lifespan. Attached Figure Description

[0040] Figure 1The catalyst (Cu) prepared in Example 1 of this invention 10 Ag) and its comparative catalysts (pure Cu, Cu) 20 Scanning electron microscope (SEM) images of Ag and Cu5Ag.

[0041] Figure 2 The catalyst (Cu) prepared in Example 1 of this invention 10 High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of Ag and corresponding elemental distribution (EDS mapping) diagram.

[0042] Figure 3 The catalyst (Cu) prepared in Example 1 of this invention 10 High-resolution transmission electron microscopy (HR-TEM) images of Ag and its control catalysts.

[0043] Figure 4 The catalyst (Cu) prepared in Example 1 of this invention 10 X-ray diffraction (XRD) patterns of Ag and its control catalysts.

[0044] Figure 5 The catalyst (Cu) prepared in Example 1 of this invention 10 Fine spectra of Cu 2p and Ag 3d in X-ray photoelectron spectroscopy (XPS) of Ag.

[0045] Figure 6 The catalyst (Cu) prepared in Example 1 of this invention 10 Ag) and its comparative catalysts at different potentials C 2+ Comparison chart of product Faraday efficiency. Detailed Implementation

[0046] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0047] Example 1: Catalyst Cu 10 Preparation of Ag

[0048] At room temperature, CuCl₂·2H₂O (170.48 mg, 1 mmol) was dissolved in 10 mL of water. NaOH aqueous solution (1 M, 40 mL) was added under stirring to allow for complete reaction. The resulting reaction system was then transferred to a 60 °C water bath, and hydrazine hydrate (1 mL) was slowly added under stirring. The reaction was allowed to proceed for 1 h, and then cooled to room temperature. An aqueous solution containing AgNO₃ (8.49 mg, 0.05 mmol) (10 mL) was added to the system, and the mixture was rapidly stirred for 30 min, with a Cu to Ag molar ratio of 20:1. By adjusting the Cu to Ag feed ratio, catalysts with different compositions could be prepared using the same method. Subsequently, NaBH₄ (20 mg) was added to the system for further treatment. After the reaction, the resulting solid product was washed, filtered, and vacuum dried to obtain the final silver-modified copper-based electrocatalyst.

[0049] Example 2: Catalyst Cu 20 Preparation of Ag

[0050] The preparation method is the same as in Example 1, except that the amount of silver nitrate used in step (3) is adjusted so that the molar ratio of copper chloride to silver nitrate is 20:1.

[0051] Example 3: Preparation of the catalyst Cu5Ag

[0052] The preparation method is the same as in Example 1, except that the amount of silver nitrate used in step (3) is adjusted so that the molar ratio of copper chloride to silver nitrate is 5:1.

[0053] Example 4 (Control Example): Preparation of Pure Cu Catalyst

[0054] The preparation method is the same as in Example 1, except that silver nitrate is not added in step (3).

[0055] Example 5: Structural and Morphological Characterization

[0056] The catalysts prepared in Examples 1-4 were structurally characterized. Figure 1 As shown, the SEM image reveals the pure Cu catalyst ( Figure 1 a) Significant particle agglomeration is observed. After the introduction of Ag, the particle size becomes finer and more uniform, with Cu... 10 Ag( Figure 1 c) It exhibits the most ideal morphology, with clear particle boundaries and a more open pore structure formed by accumulation, which is conducive to electrolyte wetting and exposure of active sites. Figure 2 EDS mapping results confirm that in Cu 10 In the Ag catalyst, Cu and Ag elements are highly uniformly distributed, indicating the formation of numerous Cu-Ag heterointerfaces. HR-TEM image ( Figure 3The data shows that in Cu 10 In Ag, lattice fringes belonging to Cu(111) and Ag(111) can be clearly observed, and the interplanar spacing of Cu(111) is expanded compared to pure Cu, proving the existence of lattice strain. XRD pattern ( Figure 4 This indicates that all Cu x Ag catalysts are all composed of metallic Cu and metallic Ag crystalline phases, without forming a distinct alloy phase. XPS fine spectroscopy ( Figure 5 The data shows that, compared to pure Cu, Cu... 10 The shift of the Cu 2p peak in Ag towards lower binding energies, while the shift of the Ag 3d peak towards higher binding energies, confirms electron transfer from Ag to Cu.

[0057] Example 6: Electrochemical Performance Testing

[0058] The catalysts prepared in Examples 1-4 were loaded onto a gas diffusion layer to form working electrodes, and their CO2RR performance was tested in a gas diffusion flow cell. The electrolyte was 1 M KOH. Figure 6 As shown, within a wide potential window of -0.9 V to -1.6 V (vs. RHE), Cu 10 Ag catalysts all exhibited the best C2₊ product selectivity. Especially at -1.2 V vs. RHE, Cu... 10 Total C of Ag 2+ The Faraday efficiency reaches 80.87%, at which point the total current density is -324.4 mA cm⁻¹. -2 In contrast, pure Cu and other proportions of Cu x The performance of Ag catalysts was significantly worse. Furthermore, Cu... 10 Ag exhibited effective inhibition of the hydrogen evolution reaction (FE(H2) < 15%) throughout the entire test potential range. For Cu... 10 After long-term stability testing, Ag was characterized again by XRD, XPS and TEM. The results showed that its crystal structure, chemical state and microstructure were basically the same as before the reaction, which proved its excellent structural stability.

[0059] Table 1 shows the catalyst Cu. 10 CO2RR under different potential conditions of Ag 2+ The Faraday efficiency of the product.

[0060]

[0061] Table 2 shows the CO2RR under different potential conditions for catalyst Cu. 2+ The Faraday efficiency of the product.

[0062]

[0063] Table 3 shows the catalyst Cu. 20 CO2RR under different potential conditions of Ag 2+ The Faraday efficiency of the product.

[0064]

[0065] Table 4 shows the CR values ​​for CO2RR under different potential conditions using Cu5Ag catalyst. 2+ The Faraday efficiency of the product.

[0066]

[0067] The pure Cu catalyst exhibited a certain C2 product generation capability across the entire test potential range, indicating that its surface can achieve basic C-C coupling processes. However, the product types were relatively dispersed; while ethylene was one of the main products, oxygen-containing multi-carbon products such as ethanol, acetate, and n-propanol, along with H2, also accounted for a certain proportion. With a negative potential shift, the proportion of multi-carbon products increased, but H2 generation simultaneously intensified, reflecting that while the system enhanced reactivity, it failed to effectively suppress the hydrogen evolution reaction, indicating electron utilization efficiency splitting. 20 In Ag catalysts, the proportion of ethylene formation increases in certain potential ranges, and multi-carbon products exhibit a certain degree of aggregation tendency. The introduction of Ag alters the surface reaction environment, regulating the formation and transformation of key intermediates and shifting the reaction pathway towards C2. However, overall, H2 still accounts for a relatively high proportion, and C1 products are not significantly weakened, indicating that the bimetallic synergistic effect has not yet reached its ideal state, and there is still room for improvement in selectivity. 10 Ag catalysts exhibit the most significant advantage in producing multi-carbon products. Around -1.2 V (vs. RHE), multi-carbon products dominate, with C2H4 and C2H5OH contributing the most. At this potential, C... 2+ The overall Faraday efficiency of the products reached 81%, with ethylene at 46.7% and ethanol at approximately 24%, while maintaining a high current density. At each potential point, ethylene and ethanol consistently occupied the majority, while CH4, CO, and HCOOH remained at lower levels, indicating no significant competing pathways. The proportion of H2 did not increase significantly, suggesting that side reactions were suppressed and electrons were mainly used for CO2 reduction. These results indicate that Cu... 10 Ag surfaces can maintain a high coverage of carbon-containing intermediates and promote their coupling to form multi-carbon products, making the reaction pathway more focused on C. 2+ Direction. In Cu5Ag catalysts, the distribution of multi-carbon products is relatively higher than that of Cu. 10Ag tends to disperse. Ethylene remains an important product, but its dominance has weakened. The proportion of oxygen-containing products and H2 has increased, indicating that when the Ag content decreases, its ability to regulate intermediate behavior and reaction pathways weakens, making it difficult to maintain an efficient multi-carbon formation environment.

[0068] The above embodiments are merely illustrative of the technical ideas and features of the present invention, and are intended to help those skilled in the art understand and implement the present invention, but should not be construed as limiting the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0069] The above embodiments are only used to illustrate the present invention. Any equivalent transformations and improvements made on the basis of the technical solutions of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. A method for preparing a silver-modified copper-based electrocatalyst, characterized in that, Includes the following steps: (1) Add NaOH aqueous solution to CuCl2 solution to allow it to react fully; the molar ratio of CuCl2 to NaOH is 1:(30-5); (2) After the reaction is complete, the resulting system is transferred to a water bath and hydrazine hydrate is slowly added. After the reaction, the system is cooled to room temperature. The molar ratio of CuCl2 to hydrazine hydrate is 1:(15-30). (3) Add a solution containing AgNO3 to the cooled reaction system. The molar ratio of Cu to Ag is (5-20):

1. (4) Then, a reducing agent, ascorbic acid or NaBH4, was added to the above system. The solid product obtained after the reaction was washed, filtered and dried under vacuum to obtain the target silver-modified copper-based electrocatalyst. The molar ratio of CuCl2 to reducing agent is 1:(0.2-0.8).

2. The preparation method according to claim 1, characterized in that: The molar ratio of copper to silver is 10:

1.

3. The preparation method according to claim 1, characterized in that: The reduction reaction was carried out in a water bath at 60 °C.

4. A silver-modified copper-based electrocatalyst, characterized in that: It is prepared by any one of the methods described in claims 1-3.

5. The application of the silver-modified copper-based electrocatalyst according to claim 4, characterized in that: The electrocatalyst is used in a gas diffusion electrode device to electrocatalyze the reduction of carbon dioxide to generate multi-carbon products.

6. The application according to claim 5, characterized in that: The multicarbon products include ethylene and ethanol.

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