A copper metal catalyst, its preparation method and use

Abstract

The application provides a metal copper catalyst and a preparation method and application thereof, the preparation method of the metal copper catalyst comprises the following steps: S1, hydrophilic modification and activation are conducted on carbon paper to obtain a carbon paper carrier; S2, a mixed solution of copper nitrate, sulfuric acid, citric acid and water is used as an electrolyte, and copper catalyst is grown on the carbon paper carrier by using an electrodeposition method; and S3, the carbon paper carrier with the grown copper catalyst is washed and dried to obtain the metal copper catalyst loaded on the carbon paper carrier. The catalyst has a high-density (110) crystal surface, significantly improves the yield of ethanol product in a CO2 reduction reaction, and meanwhile, the catalyst avoids the influence of the use of an organic capping agent on a catalytic process.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalyst technology, specifically relating to a metallic copper catalyst, its preparation method, and its application. Background Technology

[0002] The excessive use of fossil fuels has led to a year-on-year increase in atmospheric CO2 concentration, resulting in a series of environmental problems. Taking effective measures to curb CO2 emissions and promote an efficient carbon cycle is crucial for achieving the "dual carbon" goals (carbon reduction and emission reduction). Electrocatalysis can convert CO2 into high-value-added chemicals, enabling resource utilization, promoting the carbon cycle, and reducing carbon emissions. Ethanol, as one of the CO2 reduction products, has significant pharmaceutical and industrial applications. However, due to the complexity of the CO2 reduction reaction and the numerous byproducts, the current method of ethanol production using this strategy is still some distance from industrial application. Therefore, developing low-cost catalysts with high ethanol selectivity is a key step in promoting the efficient conversion of CO2 to ethanol.

[0003] Among numerous electrocatalysts, Cu is the only material capable of simultaneously converting CO2 into C1 and C2 products. The crystal facets of Cu exhibit high sensitivity to CO2 reduction products. Numerous studies have shown that the (111) crystal facet of Cu exhibits high selectivity for methane products, while the (100) crystal facet exhibits high selectivity for ethylene products. Ethanol products tend to be generated on the (110) step facet and some high-index crystal faces. However, actual studies have revealed that the ethanol production efficiency is far lower than theoretical levels. This is mainly due to two reasons: (1) The (110) crystal facet of Cu is located at the interface between the (100) and (111) crystal faces and cannot exist independently. It is difficult to obtain a large area of ​​exposure on the (110) crystal facet in experiments, which limits the selectivity of ethanol products. (2) In conventional synthesis methods, organic capping agents are often added to the reaction system to induce the exposure of special Cu crystal faces. However, the incomplete removal of these organic substances not only hinders the smooth transport of charge on the catalyst surface, but also interferes with the CO2 reduction pathway and reduces product selectivity (ACS Catal. 2021, 11, 13330-13336; ACS Nano 2016, 10, 4559-4564; ACS Catal. 2019, 9, 7894-7899; J. Phys. Chem. Lett. 2019, 10, 4259-4265; Coord. Chem. Rev. 2022, 454, 214340).

[0004] Chinese patent application CN 114134530 A discloses a method for preparing a Cu-P-100 catalyst and its application in the electrocatalytic reduction of carbon dioxide. The method uses a mixture of tannic acid and copper nitrate as the electrolyte to prepare the Cu catalyst. Although this method successfully avoids the use of organic capping agents, the resulting catalyst does not exhibit any special crystal face exposure. In the CO2 reduction reaction, it generates a mixed product containing multiple components such as carbon monoxide (CO), methane (CH4), formic acid (HCOOH), and acetic acid (CH3COOH), and no reports have been found regarding the ethanol product. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a copper catalyst, its preparation method and application. The catalyst has a high density (110) crystal facet, which significantly improves the yield of ethanol product in CO2 reduction reaction. At the same time, the catalyst avoids the influence of the use of organic capping agents on the catalytic process.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing a metallic copper catalyst, comprising:

[0008] S1, The carbon paper is modified and activated to obtain a carbon paper carrier;

[0009] S2 uses a mixture of copper nitrate, sulfuric acid, citric acid and water as the electrolyte to grow a copper catalyst on a carbon paper support by electrodeposition.

[0010] S3, the carbon paper support on which the copper catalyst is grown is washed and dried to obtain the metallic copper catalyst supported on the carbon paper support.

[0011] Preferably, in the method for preparing the copper catalyst, S1 specifically includes:

[0012] (1) The carbon paper was washed with deionized water and anhydrous ethanol to remove impurities, and then added to sulfuric acid solution and heated to obtain hydrophilic carbon paper.

[0013] (2) In the three-electrode system, sulfuric acid solution is used as electrolyte, and hydrophilic carbon paper is activated by cyclic voltammetry to obtain carbon paper carrier.

[0014] Preferably, in step (1), the heating temperature is 50~70℃ and the heating time is 50~70 min.

[0015] Preferably, in step (2), the three-electrode system uses a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, and hydrophilic carbon paper as the working electrode. The cyclic voltammetry parameters are set as follows: upper limit of potential is 0 V, lower limit is -1.7 V to -2.3 V, starting potential is 0 V, number of cycles is 6 to 8, and scan rate is 90 to 110 mV / s.

[0016] Preferably, in the method for preparing the copper catalyst, in step S2, the concentration of copper nitrate in the electrolyte is 0.005~0.05 mol / L, and the concentration of citric acid is 0.01~0.1 mol / L.

[0017] Preferably, in the method for preparing the copper catalyst, in step S2, the pH value of the electrolyte is 1 to 4.

[0018] Preferably, in the preparation method of the copper catalyst, the electrodeposition time in step S2 is 100~500 s.

[0019] Preferably, in the preparation method of the copper catalyst, in step S2, the potential applied by the electrodeposition method is -1.0 to -1.4 V.

[0020] The present invention also provides a metallic copper catalyst obtained by the preparation method described above.

[0021] The present invention also provides the application of the aforementioned copper catalyst in electrocatalytic CO2 reduction.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The preparation method of the copper catalyst of this invention uses a mixture of copper nitrate, sulfuric acid, citric acid and water as the electrolyte. During the synthesis process, citric acid and copper nitrate form a stable complex. Compared with tannic acid, citric acid has a simpler chemical structure and smaller steric hindrance. Therefore, the complex formed by citric acid and copper nitrate is more likely to self-assemble under the action of an external electric field, causing Cu atoms to align along the lower energy direction. However, the complex formed by tannic acid and copper nitrate cannot self-assemble due to the large steric hindrance, and can only form nanoparticles without fixed crystal faces during electrodeposition. During the electrodeposition process, the energies of different Cu crystal faces are Cu(111) 1.952 J / m². -2 <Cu(100)2.166 J m -2 <Cu(110)2.237 J m -2Therefore, in this invention, the (111) and (100) crystal planes of Cu grow alternately along the Z-axis, thereby forming a copper catalyst with abundant (110) crystal planes. During electrocatalytic CO2 reduction, compared with the simple (100) crystal plane, the (110) crystal plane can undergo a rapid C-C coupling process, promoting the generation of C2 products. At the same time, compared with the (111) crystal plane, the removal of H2O during the catalytic process is suppressed on the (110) crystal plane. Therefore, the selectivity of ethanol products on the (110) crystal plane is significantly improved. In addition, citric acid forms a stable complex with copper nitrate, which can also inhibit the deposition of copper nitrate and ensure the smooth progress of the electrodeposition process. The addition of sulfuric acid ensures good conductivity of the electrolyte. The catalyst described in this invention is obtained by a one-step electrodeposition method, avoiding the influence of the use of organic capping agents on the catalytic process.

[0024] Furthermore, by controlling the electrodeposition process appropriately, a hexagonal tower-shaped copper catalyst with a special morphology can be obtained. The hexagonal tower-shaped copper catalyst has a higher density of (110) crystal faces, which further improves the yield of ethanol products in the CO2 reduction reaction.

[0025] The copper catalyst described in this invention is mainly used in electrocatalytic CO2 reduction systems. In a specific embodiment of this invention, at -0.21... vs At the overpotential of RHE, the copper catalyst achieved a maximum Faraday efficiency of 78.9% for ethanol products, which is a significant improvement over other Cu-based electrocatalysts. It also showed good stability in a CO2 reduction test lasting up to 18 hours (6 cycles). Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The morphology diagrams are shown for (a) Cu-N-300, (b) Cu-C and (c) CS catalysts;

[0028] Figure 2 The morphology diagrams are shown for (a, b) Cu-N-100 and (c, d) Cu-N-500 catalysts.

[0029] Figure 3 The atomic arrangement of the Cu-N-300 catalyst was observed under a double aberration-corrected microscope.

[0030] Figure 4XRD patterns of Cu-N series catalysts, Cu-C, and CS catalysts are shown.

[0031] Figure 5 This is a diagram showing the proportion of different crystal planes in Cu-N series catalysts and Cu-C and CS catalysts.

[0032] Figure 6 These are images of catalyst morphology obtained under different synthesis conditions.

[0033] Figure 7 The images show the morphology of catalysts obtained by electrodeposition with tannic acid as a complexing agent in (a) on unactivated carbon paper, (b) on copper foil, and (c) on copper foil.

[0034] Figure 8 The distribution of electrocatalytic CO2 reduction products of (a) Cu-N-300 and (b) Cu-C and (c) CS catalysts at different overpotentials is shown in the figure.

[0035] Figure 9 The distribution of electrocatalytic CO2 reduction products of the catalysts obtained in different embodiments and comparative examples at the optimal overpotential is shown in the diagram.

[0036] Figure 10 The graph shows the cycle stability test results of the Cu-N-300 catalyst for electrocatalytic CO2 reduction. Detailed Implementation

[0037] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0038] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0039] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not intended to limit the order of the method steps or define the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0040] The present invention discloses a method for preparing a copper catalyst, which uses copper nitrate as a precursor and grows the copper catalyst on the surface of hydrophilic carbon paper by a one-step electrodeposition method.

[0041] Specifically, the preparation method of the copper catalyst of the present invention includes:

[0042] S1, The carbon paper is modified and activated to obtain a carbon paper carrier;

[0043] S2 uses a mixture of copper nitrate, sulfuric acid, citric acid and water as the electrolyte to grow a copper catalyst on a carbon paper support by electrodeposition.

[0044] S3, the carbon paper support on which the copper catalyst is grown is washed and dried to obtain the metallic copper catalyst supported on the carbon paper support.

[0045] The method for preparing the copper catalyst of the present invention uses a mixture of copper nitrate, sulfuric acid, citric acid and water as electrolyte and carbon paper as carrier. The copper catalyst with abundant (110) crystal planes can be controllably grown on the carbon paper carrier by electrodeposition. Compared with the (111) crystal plane, the removal of H2O during the catalytic process on the (110) crystal plane in the CO2 reduction reaction is suppressed. Therefore, the selectivity of ethanol products on the (110) crystal plane is significantly improved.

[0046] The specific preparation method of the carbon paper carrier described in S1 of this invention includes the following steps:

[0047] (1) The carbon paper was washed with deionized water and anhydrous ethanol to remove impurities, and then added to sulfuric acid solution and heated to obtain hydrophilic carbon paper.

[0048] Specifically: the cleaning method used for cleaning the carbon paper is ultrasonic cleaning, with an ultrasonic time of 8~12 min; the concentration of the sulfuric acid solution is 0.9~1.1 mol / L, the heating temperature is 50~70℃, and the heating time is 50~70 min.

[0049] (2) In the three-electrode system, sulfuric acid solution is used as electrolyte, and hydrophilic carbon paper is activated by cyclic voltammetry to obtain carbon paper carrier.

[0050] Specifically, the three-electrode system mainly consists of: a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, carbon paper as the working electrode, and a 0.45~0.55 mol / L sulfuric acid solution as the electrolyte; the cyclic voltammetry parameters are set as follows: upper limit of potential is 0 V, lower limit is -1.7 V to -2.3 V, initial potential is 0 V, number of cycles is 6~8, and scan rate is 90~110 mV / s.

[0051] In S2 of this invention, a copper catalyst is grown on a carbon paper support using an electrodeposition method, specifically including the following steps:

[0052] (1) Prepare electrolyte using copper nitrate, concentrated sulfuric acid and citric acid as precursors.

[0053] Specifically: in the electrolyte, the concentration of copper nitrate is 0.005~0.05 mol / L, more preferably 0.01 mol / L; the concentration of citric acid is 0.01~0.1 mol / L, preferably 0.04~0.06 mol / L, more preferably 0.05 mol / L; the solution mixing and stirring time is 25~35 min; and the pH of the electrolyte is 1~4, preferably pH 4.

[0054] (2) Copper catalysts were grown on carbon paper support by chronoamperometry.

[0055] Specifically, the electrolyte in step (1) is used as the electrolyte, carbon paper carrier is used as the working electrode, Pt sheet is used as the counter electrode, and Ag / AgCl electrode is used as the reference electrode. A potential of -1.0 to -1.4 V is applied to perform electrodeposition. The electrodeposition time is 100 to 500 s, more preferably 250 to 350 s, and the electrodeposition temperature is 20 to 30 ℃.

[0056] In step S3 of this invention, the washing process involves rinsing the product with running water for 45-75 seconds; the drying temperature is 55-65°C, and the drying time is 16-24 hours.

[0057] The method for preparing the copper catalyst of this invention uses citric acid as a complexing agent, which allows Cu atoms to align along the lower energy direction, thereby forming a copper catalyst with abundant (110) crystal planes. During electrocatalytic CO2 reduction, compared to the simple (100) crystal plane, the (110) crystal plane enables a rapid C-C coupling process, promoting the formation of C2 products. Simultaneously, compared to the (111) crystal plane, the removal of H2O during catalysis is suppressed on the (110) crystal plane. Therefore, the selectivity of the ethanol product on the (110) crystal plane is significantly improved. Furthermore, the stable complex formed by citric acid and copper nitrate enhances the stability of the electrolyte, ensuring a smooth electrodeposition process. Adding an appropriate amount of sulfuric acid can improve the conductivity of the electrolyte.

[0058] The copper catalyst prepared by the method described in this invention consists only of elemental copper. When the electrodeposition time is controlled at 300 s, the catalyst exhibits a unique hexagonal pyramidal structure. This structure is formed by a large number of alternating (100) and (111) crystal planes stacked together, with abundant (110) crystal planes formed at the interface between the two crystal planes. The catalyst of this invention exhibits excellent ethanol product selectivity in the electrocatalytic CO2 reduction reaction, with a Faraday efficiency of 46.2% to 78.9%.

[0059] Example 1

[0060] Hexagonal tower-shaped Cu-N-300 catalyst was prepared according to the preparation method proposed in this invention:

[0061] (1) Clean the 1×1.5 cm carbon paper with deionized water and anhydrous ethanol by ultrasonication for 10 min, and then treat it with sulfuric acid at 60℃ for 60 min to obtain hydrophilic carbon paper.

[0062] (2) Hydrophilic carbon paper was activated in a three-electrode system using cyclic voltammetry to obtain a carbon paper carrier: The three-electrode system consisted of a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, hydrophilic carbon paper as the working electrode, and a 0.5 mol / L sulfuric acid solution as the electrolyte; The cyclic voltammetry parameters were set as follows: the upper limit of potential was 0 V, the lower limit was -2.0 V, the initial potential was 0 V, the number of cycles was 7, and the scan rate was 100 mV / s.

[0063] (3) Add copper nitrate, citric acid and concentrated sulfuric acid to 30 mL of water to prepare an electrolyte. The concentrations of different substances in the electrolyte are 0.01 mol / L copper nitrate, 1 mol / L sulfuric acid and 0.05 mol / L citric acid. The components are stirred in water for 30 min to dissolve completely to obtain an electrolyte with a pH of 4.

[0064] (4) Using the carbon paper support obtained in step (2) as the working electrode, Pt sheet as the counter electrode, and Ag / AgCl electrode as the reference electrode, electrodeposition is performed in the electrolyte obtained in step (3). The constant voltage deposition is performed at a potential of -1.2V for 300s to obtain Cu catalyst loaded on carbon paper.

[0065] (5) Take out the electrodeposited sample and rinse it with running water for 1 min to obtain Cu-N-300 catalyst material that can be used for electrocatalytic reaction.

[0066] The catalyst morphology obtained in Example 1 is as follows: Figure 1 As shown in a, the product Faradaic efficiency of the catalyst in the electrocatalytic CO2 reduction reaction at different overpotentials is as follows: Figure 5 As shown in a, the Faraday efficiency for ethanol in the electrocatalytic CO2 reduction reaction can reach up to 79.8%.

[0067] Example 2

[0068] (1) Clean the 1×1.5 cm carbon paper with deionized water and anhydrous ethanol by ultrasonication for 10 min, and then treat it with sulfuric acid at 60℃ for 60 min to obtain hydrophilic carbon paper.

[0069] (2) Hydrophilic carbon paper was activated in a three-electrode system using cyclic voltammetry to obtain a carbon paper carrier: The three-electrode system consisted of a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, hydrophilic carbon paper as the working electrode, and a 0.5 mol / L sulfuric acid solution as the electrolyte; The cyclic voltammetry parameters were set as follows: the upper limit of potential was 0 V, the lower limit was -2.0 V, the initial potential was 0 V, the number of cycles was 7, and the scan rate was 100 mV / s.

[0070] (3) Add copper nitrate, citric acid and concentrated sulfuric acid to 30 mL of water to prepare an electrolyte. The concentrations of different substances in the electrolyte are 0.01 mol / L copper nitrate, 1 mol / L sulfuric acid and 0.05 mol / L citric acid. The components are stirred in water for 30 min to dissolve completely to obtain an electrolyte with a pH of 4.

[0071] (4) Using the carbon paper support obtained in step (2) as the working electrode, the Pt sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode, electrodeposition was performed in the electrolyte obtained in step (3). The constant voltage deposition was carried out for 100s at a potential of -1.2V to obtain the Cu catalyst loaded on the carbon paper.

[0072] (5) Take out the electrodeposited sample and rinse it with running water for 1 min to obtain Cu-N-100 catalyst material that can be used for electrocatalytic reaction.

[0073] The catalyst Cu-N-100 obtained in Example 2 has a Faraday efficiency of 46.2% for ethanol in the electrocatalytic CO2 reduction reaction.

[0074] Example 3

[0075] (1) Clean the 1×1.5 cm carbon paper with deionized water and anhydrous ethanol by ultrasonication for 10 min, and then treat it with sulfuric acid at 60℃ for 60 min to obtain hydrophilic carbon paper.

[0076] (2) Hydrophilic carbon paper was activated in a three-electrode system using cyclic voltammetry to obtain a carbon paper carrier: The three-electrode system consisted of a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, hydrophilic carbon paper as the working electrode, and a 0.5 mol / L sulfuric acid solution as the electrolyte; The cyclic voltammetry parameters were set as follows: the upper limit of potential was 0 V, the lower limit was -2.0 V, the initial potential was 0 V, the number of cycles was 7, and the scan rate was 100 mV / s.

[0077] (3) Add copper nitrate, citric acid and concentrated sulfuric acid to 30 mL of water to prepare an electrolyte. The concentrations of different substances in the electrolyte are 0.01 mol / L copper nitrate, 1 mol / L sulfuric acid and 0.05 mol / L citric acid. The components are stirred in water for 30 min to dissolve completely to obtain an electrolyte with a pH of 4.

[0078] (4) Using the carbon paper support obtained in step (2) as the working electrode, Pt sheet as the counter electrode, and Ag / AgCl electrode as the reference electrode, electrodeposition is performed in the electrolyte obtained in step (3). The Cu catalyst loaded on the carbon paper is obtained by constant voltage deposition for 500s at a potential of -1.2V.

[0079] (5) Take out the electrodeposited sample and rinse it with running water for 1 min to obtain the catalyst material Cu-N-500 that can be used for electrocatalytic reaction.

[0080] The catalyst Cu-N-500 obtained in this embodiment has a Faraday efficiency of 57.5% for ethanol in the electrocatalytic CO2 reduction reaction.

[0081] Example 4

[0082] (1) Clean the 1×1.5 cm carbon paper with deionized water and anhydrous ethanol by ultrasonication for 10 min, and then treat it with sulfuric acid at 60℃ for 60 min to obtain hydrophilic carbon paper.

[0083] (2) Hydrophilic carbon paper was activated in a three-electrode system using cyclic voltammetry to obtain a carbon paper carrier: The three-electrode system consisted of a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, hydrophilic carbon paper as the working electrode, and a 0.5 mol / L sulfuric acid solution as the electrolyte; The cyclic voltammetry parameters were set as follows: the upper limit of potential was 0 V, the lower limit was -2.0 V, the initial potential was 0 V, the number of cycles was 7, and the scan rate was 100 mV / s.

[0084] (3) Add copper nitrate, citric acid and concentrated sulfuric acid to 30 mL of water to prepare an electrolyte. The concentrations of different substances in the electrolyte are 0.01 mol / L copper nitrate, 0.1 mol / L sulfuric acid and 0.05 mol / L citric acid. The components are stirred in water for 30 min to dissolve completely to obtain an electrolyte with a pH of 1.

[0085] (4) Using the carbon paper support obtained in step (2) as the working electrode, the Pt sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode, electrodeposition was performed in the electrolyte obtained in step (3). The Cu catalyst loaded on the carbon paper was obtained by constant voltage deposition for 300s at a potential of -1.2V.

[0086] (5) Remove the electrodeposited sample and rinse it with running water for 1 min to obtain the catalyst material Cu-N. i4 .

[0087] Figure 6 The scanning electron microscopy results in (a) show that the Cu catalyst obtained under the conditions of this embodiment mainly exhibits the morphology of nanoparticles.

[0088] Example 5

[0089] (1) Clean the 1×1.5 cm carbon paper with deionized water and anhydrous ethanol by ultrasonication for 10 min, and then treat it with sulfuric acid at 60℃ for 60 min to obtain hydrophilic carbon paper.

[0090] (2) Hydrophilic carbon paper was activated in a three-electrode system using cyclic voltammetry to obtain a carbon paper carrier: The three-electrode system consisted of a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, hydrophilic carbon paper as the working electrode, and a 0.5 mol / L sulfuric acid solution as the electrolyte; The cyclic voltammetry parameters were set as follows: the upper limit of potential was 0 V, the lower limit was -2.0 V, the initial potential was 0 V, the number of cycles was 7, and the scan rate was 100 mV / s.

[0091] (3) Add copper nitrate, citric acid and concentrated sulfuric acid to 30 mL of water to prepare an electrolyte. The concentrations of different substances in the electrolyte are 0.01 mol / L copper nitrate, 0.005 mol / L sulfuric acid and 0.05 mol / L citric acid. The components are stirred in water for 30 min to dissolve completely to obtain an electrolyte with a pH of 2.

[0092] (4) Using the carbon paper support obtained in step (2) as the working electrode, the Pt sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode, electrodeposition was performed in the electrolyte obtained in step (3). The Cu catalyst loaded on the carbon paper was obtained by constant voltage deposition for 300s at a potential of -1.2V.

[0093] (5) Remove the electrodeposited sample and rinse it with running water for 1 min to obtain the catalyst material Cu-N. i5 .

[0094] Figure 6 The scanning electron microscopy results in (b) show that the Cu catalyst obtained under the conditions of this embodiment mainly exhibits an agglomerated blocky structure.

[0095] Example 6

[0096] (1) Clean the 1×1.5 cm carbon paper with deionized water and anhydrous ethanol by ultrasonication for 10 min, and then treat it with sulfuric acid at 60℃ for 60 min to obtain hydrophilic carbon paper.

[0097] (2) Hydrophilic carbon paper was activated in a three-electrode system using cyclic voltammetry to obtain a carbon paper carrier: The three-electrode system consisted of a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, hydrophilic carbon paper as the working electrode, and a 0.5 mol / L sulfuric acid solution as the electrolyte; The cyclic voltammetry parameters were set as follows: the upper limit of potential was 0 V, the lower limit was -2.0 V, the initial potential was 0 V, the number of cycles was 7, and the scan rate was 100 mV / s.

[0098] (3) Add copper nitrate, citric acid and concentrated sulfuric acid to 30 mL of water to prepare an electrolyte. The concentrations of different substances in the electrolyte are 0.01 mol / L copper nitrate, 1 mol / L sulfuric acid and 0.01 mol / L citric acid. The above components are stirred in water for 30 min to dissolve completely to obtain an electrolyte with a pH of 4.

[0099] (4) Using the carbon paper support obtained in step (2) as the working electrode, the Pt sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode, electrodeposition was performed in the electrolyte obtained in step (3). The Cu catalyst loaded on the carbon paper was obtained by constant voltage deposition for 300s at a potential of -1.2V.

[0100] (5) Remove the electrodeposited sample and rinse it with running water for 1 min to obtain the catalyst material Cu-N. i6 .

[0101] Figure 6The scanning electron microscopy results in (c) show that the Cu catalyst obtained under the conditions of this embodiment mainly exhibits the morphology of random nanosheets.

[0102] Example 7

[0103] (1) Clean the 1×1.5 cm carbon paper with deionized water and anhydrous ethanol by ultrasonication for 10 min, and then treat it with sulfuric acid at 60℃ for 60 min to obtain hydrophilic carbon paper.

[0104] (2) Hydrophilic carbon paper was activated in a three-electrode system using cyclic voltammetry to obtain a carbon paper carrier: The three-electrode system consisted of a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, hydrophilic carbon paper as the working electrode, and a 0.5 mol / L sulfuric acid solution as the electrolyte; The cyclic voltammetry parameters were set as follows: the upper limit of potential was 0 V, the lower limit was -2.0 V, the initial potential was 0 V, the number of cycles was 7, and the scan rate was 100 mV / s.

[0105] (3) Add copper nitrate, citric acid and concentrated sulfuric acid to 30 mL of water to prepare an electrolyte. The concentrations of different substances in the electrolyte are 0.01 mol / L copper nitrate, 1 mol / L sulfuric acid and 0.1 mol / L citric acid. The components are stirred in water for 30 min to dissolve completely to obtain an electrolyte with a pH of 4.

[0106] (4) Using the carbon paper support obtained in step (2) as the working electrode, the Pt sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode, electrodeposition was performed in the electrolyte obtained in step (3). The Cu catalyst loaded on the carbon paper was obtained by constant voltage deposition for 300s at a potential of -1.2V.

[0107] (5) Remove the electrodeposited sample and rinse it with running water for 1 min to obtain the catalyst material Cu-N. i7 .

[0108] Figure 6 The scanning electron microscopy results in (d) show that the Cu catalyst obtained under the conditions of this embodiment mainly exhibits the morphology of randomly aggregated nanosheets.

[0109] Example 8

[0110] (1) Clean the 1×1.5 cm carbon paper with deionized water and anhydrous ethanol by ultrasonication for 10 min, and then treat it with sulfuric acid at 60℃ for 60 min to obtain hydrophilic carbon paper.

[0111] (2) Hydrophilic carbon paper was activated in a three-electrode system using cyclic voltammetry to obtain a carbon paper carrier: The three-electrode system consisted of a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, hydrophilic carbon paper as the working electrode, and a 0.5 mol / L sulfuric acid solution as the electrolyte; The cyclic voltammetry parameters were set as follows: the upper limit of potential was 0 V, the lower limit was -2.0 V, the initial potential was 0 V, the number of cycles was 7, and the scan rate was 100 mV / s.

[0112] (3) Add copper nitrate, citric acid and concentrated sulfuric acid to 30 mL of water to prepare an electrolyte. The concentrations of different substances in the electrolyte are 0.005 mol / L copper nitrate, 1 mol / L sulfuric acid and 0.05 mol / L citric acid. The above components are stirred in water for 30 min to dissolve completely to obtain an electrolyte with a pH of 4.

[0113] (4) Using the carbon paper support obtained in step (2) as the working electrode, the Pt sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode, electrodeposition was performed in the electrolyte obtained in step (3). The Cu catalyst loaded on the carbon paper was obtained by constant voltage deposition for 300s at a potential of -1.2V.

[0114] (5) Remove the electrodeposited sample and rinse it with running water for 1 min to obtain the catalyst material Cu-N. i8 .

[0115] Figure 6 The scanning electron microscopy results in (e) show that the Cu catalyst obtained under the conditions of this embodiment not only exhibits a regular hexagonal pyramidal structure, but also contains a large number of nanoparticles.

[0116] Example 9

[0117] (1) Clean the 1×1.5 cm carbon paper with deionized water and anhydrous ethanol by ultrasonication for 10 min, and then treat it with sulfuric acid at 60℃ for 60 min to obtain hydrophilic carbon paper.

[0118] (2) Hydrophilic carbon paper was activated in a three-electrode system using cyclic voltammetry to obtain a carbon paper carrier: The three-electrode system consisted of a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, hydrophilic carbon paper as the working electrode, and a 0.5 mol / L sulfuric acid solution as the electrolyte; The cyclic voltammetry parameters were set as follows: the upper limit of potential was 0 V, the lower limit was -2.0 V, the initial potential was 0 V, the number of cycles was 7, and the scan rate was 100 mV / s.

[0119] (3) Add copper nitrate, citric acid and concentrated sulfuric acid to 30 mL of water to prepare an electrolyte. The concentrations of different substances in the electrolyte are 0.05 mol / L copper nitrate, 1 mol / L sulfuric acid and 0.01 mol / L citric acid. The components are stirred in water for 30 min to dissolve completely to obtain an electrolyte with a pH of 4.

[0120] (4) Using the carbon paper support obtained in step (2) as the working electrode, the Pt sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode, electrodeposition was performed in the electrolyte obtained in step (3). The Cu catalyst loaded on the carbon paper was obtained by constant voltage deposition for 300s at a potential of -1.2V.

[0121] (5) Remove the electrodeposited sample and rinse it with running water for 1 min to obtain the catalyst material Cu-N. i9 .

[0122] Figure 6 The scanning electron microscopy results in (f) show that the Cu catalyst obtained under the conditions of this embodiment exhibits a large number of assembled pine cone structures.

[0123] Comparative Example 1

[0124] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that copper nitrate is replaced with copper chloride to prepare Cu-C catalyst.

[0125] The morphology and structure of the obtained Cu-C catalyst are as follows: Figure 1 As shown in Figure b, the catalyst has a Faraday efficiency of 38.8% for ethanol in the electrocatalytic CO2 reduction reaction.

[0126] Comparative Example 2

[0127] The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that copper nitrate is replaced with copper sulfate to prepare Cu-S catalyst.

[0128] The morphology and structure of the obtained Cu-S catalyst are as follows: Figure 1 As shown in Figure c, the catalyst has a Faraday efficiency of 20.3% for ethanol in the electrocatalytic CO2 reduction reaction.

[0129] Comparative Example 3

[0130] The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that: unactivated carbon paper is used as a carrier for electrodeposition. The experiment found that the unactivated carbon paper is hydrophobic and cannot grow Cu catalyst by electrodeposition.

[0131] Comparative Example 4

[0132] The preparation method of Comparative Example 4 is basically the same as that of Example 1, except that carbon paper activated only by sulfuric acid is used as a carrier for electrodeposition to prepare Cu-N. c4 catalyst.

[0133] Comparative Example 5

[0134] The preparation method of Comparative Example 5 is basically the same as that of Example 1, except that: carbon paper activated only by electrochemical means is used as a carrier for electrodeposition to prepare Cu-N. c5 catalyst.

[0135] Comparative Example 6

[0136] The preparation method of Comparative Example 6 is basically the same as that of Example 1, except that copper foil is used as the carrier instead of carbon paper for electrodeposition to prepare Cu-N. c6 catalyst.

[0137] Comparative Example 7

[0138] The preparation method of Comparative Example 7 is basically the same as that of Example 1, except that citric acid is replaced with tannic acid for electrodeposition to prepare Cu-N. c7 catalyst.

[0139] like Figure 1 As shown, a, b, and c are scanning electron microscope (SEM) images of the catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively. From... Figure 1 It can be seen that when different copper sources are used for electrodeposition, only copper nitrate precursor can induce the formation of hexagonal tower-like structures. In contrast, when copper sulfate is used as a precursor, the resulting catalyst mainly exhibits a plate-like structure, while when copper chloride is used as a precursor, the resulting catalyst exhibits a stacked nano-dendritic structure.

[0140] Figure 2 Scanning electron microscope (SEM) images of the catalysts prepared in Examples 2 and 3 are shown. From Figure 2 It can be seen that the evolution of the hexagonal pyramidal structure is closely related to the electrodeposition time. When the deposition time is short, the catalyst is mainly irregular polygonal nanoparticles, while when the deposition time is long, the stacked hexagonal pyramidal structure is further assembled to form a three-dimensional structure similar to a pine cone.

[0141] Figure 3 A high-resolution atomic arrangement diagram of the catalyst prepared in Example 1 is shown. From Figure 3 As can be seen, the hexagonal pyramidal structure obtained in Example 1 exposes a large number of (111) and (100) crystal planes, with a large number of (110) crystal planes forming at the interface between the two types of crystal planes. Furthermore, through... Figure 4Analysis shows that the catalyst Cu-N-300 prepared in Example 1, like the catalysts in Comparative Examples 1 and 2, is mainly elemental copper, with a small amount of Cu2O forming on the catalyst surface. Figure 5 As can be seen, the proportions of catalyst crystal faces obtained under different precursor types and different electrodeposition times show significant differences. Since the (110) and (100) crystal faces of Cu cannot be directly displayed on XRD, they are represented by their corresponding (220) and (200) crystal faces, respectively. Figure 5 It can be seen that, compared with the catalysts of Comparative Examples 1 and 2, the (110) crystal plane of the Cu-N-300 catalyst in Example 1 has a higher proportion; compared with Examples 2 and 3, the (110) crystal plane of the Cu-N-300 catalyst in Example 1 has a higher proportion. The above analysis results show that the type of precursor and the electrodeposition time not only affect the crystal plane composition of Cu catalyst, but also affect the morphology of the catalyst and the geometric relationship between different crystal planes.

[0142] Figure 6 These are morphology diagrams of the catalysts obtained under different electrolyte conditions. The Cu-N catalysts from Examples 4 and 5 are shown. i4 and Cu-N i5 As can be seen, the concentration of sulfuric acid not only affects the pH of the electrolyte but also the deposition and growth behavior of Cu. Specifically, when the sulfuric acid concentration is 0.1 mol / L, large-area cracks appear on the carbon paper surface, reducing deposition uniformity; when the sulfuric acid concentration is 0.005 mol / L, the sample exhibits a large-area aggregation state. Secondly, regarding the Cu-N catalysts in Examples 6 and 7… i6 and Cu-N i7 As can be seen, when the concentration of citric acid is too low or too high, the samples exhibit a turtle-like nanosheet or aggregated state. From the Cu-N catalysts of Examples 8 and 9... i8 and Cu-N i9 As can be seen, when the copper nitrate concentration is too low, a large number of unassembled nanoparticles appear in the sample, while excessively high concentrations of copper nitrate lead to the formation of large-scale, excessively self-assembled pine cone-like structures. Meanwhile, the catalysts Cu-N from comparative examples 4 and 5... c4 and Cu-N c5 As can be seen, almost no Cu catalyst deposition can be found on carbon paper activated by a single method. Figure 7 The results show that, from the scanning electron microscope images of the catalyst in Comparative Example 3, copper catalysts could not be produced on unactivated carbon paper (a); when copper foil was used as a support, a self-assembled hexagonal tower-like structure could not be obtained (b); and when tannic acid was used as a complexing agent, the sample exhibited an irregular nanosphere structure (c).

[0143] The electrocatalytic performance of the catalyst for CO2 reaction was tested using a three-electrode system in the Chenhua electrochemical workstation. Carbon paper loaded with Cu catalyst was used as the working electrode, a Pt sheet as the counter electrode, and an Hg / HgO electrode as the reference electrode. A 1M KHCO3 solution was used as the electrolyte. Before the reaction, CO2 was introduced into the electrode solution at a flow rate of 100 mL / min for 30 min to saturate it. During the reaction, CO2 was continuously introduced into the system at a flow rate of 6 mL / min, and the reaction was carried out at a specific potential for 3 hours. After the reaction, liquid and gaseous products were collected separately, and their components were analyzed by chromatography. CO and CH4 in the gaseous products were detected by TCD, H2 by FID1, and the liquid products were detected by FID2 detector equipped with a column.

[0144] The product distributions of the catalysts in Examples 1, 1, and 2 at different potentials are shown below. Figure 8 As shown, the product distribution of all catalysts at -0.215V is as follows: Figure 9 As shown. By comparing the experimental results of Comparative Examples 1 and 2 with those of Example 1, it can be found that when copper nitrate is used as a precursor, the copper catalyst obtained has better selectivity for ethanol products than that of copper sulfate and copper chloride precursors. At the same time, by comparing the results of Examples 1 to 3, it can be seen that when the catalyst forms a regular hexagonal pyramidal structure, the catalyst has the best selectivity for ethanol products. This is because in the formed hexagonal pyramidal structure, the alternating exposure of (100) and (111) crystal faces results in the formation of abundant (110) crystal faces in the catalyst. Compared with the (100) and (111) crystal faces, the (110) crystal faces formed at the (100) and (111) interfaces are beneficial to C-C coupling and can suppress the dehydration process to a certain extent, thereby significantly improving the formation of C2 product ethanol.

[0145] Figure 10 This is a graph showing the electrocatalytic CO2 reduction cycle stability test of catalyst Cu-N-300 in Example 1. From... Figure 10 It can be seen that the catalyst Cu-N-300 exhibits good stability during the 18-hour CO2 reduction test.

[0146] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still make modifications or equivalent substitutions to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention pending approval.

Claims

1. A method for preparing a metallic copper catalyst, characterized in that, include: S1, The carbon paper is modified and activated to obtain a carbon paper carrier; S2, using a mixture of copper nitrate, sulfuric acid, citric acid and water as the electrolyte, a copper catalyst is grown on a carbon paper support by electrodeposition. S3, the carbon paper support on which the copper catalyst is grown is washed and dried to obtain the metallic copper catalyst supported on the carbon paper support.

2. The method for preparing the metallic copper catalyst according to claim 1, characterized in that, S1 specifically includes: (1) The carbon paper was washed with deionized water and anhydrous ethanol to remove impurities, and then added to sulfuric acid solution and heated to obtain hydrophilic carbon paper. (2) In the three-electrode system, sulfuric acid solution is used as electrolyte, and hydrophilic carbon paper is activated by cyclic voltammetry to obtain carbon paper carrier.

3. The method for preparing the metallic copper catalyst according to claim 2, characterized in that, In step (1), the heating temperature is 50~70℃ and the heating time is 50~70 min.

4. The method for preparing the metallic copper catalyst according to claim 2, characterized in that, In step (2), the three-electrode system uses a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, and hydrophilic carbon paper as the working electrode. The cyclic voltammetry parameters are set as follows: upper limit of potential is 0 V, lower limit is -1.7 V to -2.3 V, starting potential is 0 V, number of cycles is 6 to 8, and scan rate is 90 to 110 mV / s.

5. The method for preparing the metallic copper catalyst according to claim 1, characterized in that, In S2, the concentration of copper nitrate in the electrolyte is 0.005~0.05 mol / L, and the concentration of citric acid is 0.01~0.1 mol / L.

6. The method for preparing the metallic copper catalyst according to claim 1, characterized in that, In S2, the pH value of the electrolyte is 1~4.

7. The method for preparing the metallic copper catalyst according to claim 1, characterized in that, In S2, the electrodeposition time is 100~500 s.

8. The method for preparing the metallic copper catalyst according to claim 1, characterized in that, In S2, the potential applied by the electrodeposition method is -1.0 to -1.4 V.

9. A metallic copper catalyst obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the metallic copper catalyst according to claim 9 in electrocatalytic CO2 reduction.

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