Single-atom catalyst for electrocatalytic carbon dioxide reduction and preparation method

Abstract

The present invention provides a single-atom catalyst for electrocatalytic carbon dioxide reduction and a preparation method thereof. This method primarily utilizes g-C3N4 as a nitrogen source, Zn powder as a metal source, and multi-walled carbon nanotubes as a substrate. A high-density, pentacoordinated Zn-based single-atom catalyst (#imgabs0#) is designed and synthesized through a calcination process. Unlike conventional metal-N4 configurations, the novel ZnN5 configuration, due to the axial pyrrolic nitrogen, positions the Zn atom within a concave surface coplanar with four pyridinic nitrogen atoms, weakening the metal Zn's ability to serve as an active site for CO2 binding. Throughout the CO2 reduction reaction, the ZnN5 exhibits a unique structural vibrational state, where the metal Zn continuously forms and breaks bonds with the pyridinic and pyrrolic nitrogen atoms, exposing the nitrogen active sites and thus achieving the high selectivity and activity of this novel single-atom catalyst (#imgabs1#).

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalytic CO2 reduction, and specifically relates to a single-atom catalyst for electrocatalytic carbon dioxide reduction and a preparation method thereof. Background Art

[0002] The electrocatalytic reduction of carbon dioxide to chemical feedstocks offers a promising strategy for improving global carbon balance. However, due to the low kinetics of the electrocatalytic CO2 reduction reaction and the severe side reactions associated with it, the development of catalysts with both high catalytic activity and high selectivity for the CO2 reduction reaction remains a goal.

[0003] Key research areas in electrocatalytic CO2 reduction are the modification of existing catalysts and the understanding of their structure-activity relationships. By adjusting the size, structure, morphology, and composition of various catalysts, the performance of metals, metal oxides, carbon materials, and molecular compounds in CO2 electroreduction has been significantly improved. However, existing electrocatalytic CO2 reduction catalysts still have significant room for improvement in terms of catalytic efficiency, byproducts, environmental friendliness, and process operation. The development of electrocatalytic CO2 reduction materials that combine high catalytic efficiency, high byproducts, environmental friendliness, and industrial-scale production capabilities is currently a key area of research. Summary of the Invention

[0004] In light of this, the present invention aims to provide a single-atom catalyst for the electrocatalytic carbon dioxide reduction reaction and a method for its preparation. This innovative approach proposes a new approach using coordinated atoms as active sites in single-atom catalysts. This electrocatalytic carbon dioxide reduction material exhibits excellent CO selectivity and high activity, resulting in a product with high utilization value. The preparation conditions are easily controlled, simple, environmentally friendly, safe, and reproducible.

[0005] The technical solution of the present invention is: a single-atom catalyst for electrocatalytic carbon dioxide reduction, characterized in that: the single-atom catalyst is an electrocatalytic material It includes using MWCNTs as the conductive body and supplementing the nitrogen content of MWCNTs with g-C3N4 as a nitrogen source for anchoring metallic zinc; designing and synthesizing a high-density five-coordinated new configuration Zn-based single-atom catalyst on multi-walled carbon nanotubes (MWCNTs), and the ZnN5 configuration is in a vibration state during the CO2 reduction reaction.

[0006] Furthermore, the The difference from the regular M-N4 is: It is composed of Zn atoms containing four pyridinic nitrogens in the same plane and one pyrrolic nitrogen in the axial direction; Zn has a larger atomic radius and is pulled by the axial pyrrolic nitrogen, so that the Zn atom is in the concave surface of the four pyridinic nitrogen coplanar.

[0007] Furthermore, the Pass ICP test, The metal content reaches 0.54wt%, High-density single atoms are shown in spherical aberration electron microscopy.

[0008] Furthermore, the ZnN5 configuration is in a vibration state during the CO2 reduction reaction. Specifically, the Zn atom in the ZnN5 configuration is located in a concave surface coplanar with four pyridinic N atoms, which weakens the function of the Zn atom as an active site to combine with CO2. During the entire CO2RR reaction, ZnN5 presents a special state of structural vibration. In this special state, the metal Zn continuously forms and breaks bonds with pyridinic nitrogen and pyrrolic nitrogen, exposing the N active site and realizing the transfer of the active site from the metal center to the coordination atom in the single-atom catalyst.

[0009] Another technical solution of the present invention is: a method for preparing a single-atom catalyst for electrocatalytic carbon dioxide reduction, characterized in that:

[0010] (1) A certain amount of g-C3N4 was synthesized in advance, and then g-C3N4 and MWCNTs were added to the aqueous solution to obtain MWCNTs / g-C3N4 through ultrasonication and stirring.

[0011] (2) MWCNTs / g-C3N4 and zinc powder are then physically ground and mixed in a certain proportion and calcined to obtain the target single-atom dispersed catalyst with ZnN5 configuration.

[0012] This synthesis method primarily leverages the excellent conductivity of MWCNTs and the abundant nitrogen source in g-C3N4 for electron transport and subsequent metal anchoring, respectively. Furthermore, zinc has low melting points (692K) and boiling points (1180K), making it volatile at high temperatures and difficult to incorporate into the carbon structure. Therefore, the addition of g-C3N4 significantly increases both the Zn and N contents, demonstrating that g-C3N4 effectively replenishes the nitrogen source and anchors the metal, preventing metal loss.

[0013] Furthermore, the preparation of g-C3N4 and MWCNTs / g-C3N4 is as follows: 10-15g of urea is placed in a crucible, which is then placed in a muffle furnace for calcination. The conditions are: heating from room temperature to 550°C at a heating rate of 5°C / min, and maintaining at 550°C for 4h, followed by natural cooling to obtain g-C3N4. Then, g-C3N4 and MWCNTs are prepared into a mixed suspension, which is ultrasonicated for 1h, stirred for 12h, filtered, and dried at 60°C. The mass ratio of the g-C3N4 to the MWCNTs is 1:1, the specific mass is 25-30mg of g-C3N4, 25-30mg of MWCNTs, and the amount of ultrapure water is 50mL.

[0014] Further, The specific preparation is as follows: MWCNTs / g-C3N4 and zinc powder are ground evenly in a mass ratio of 2:1 and placed in a tube furnace. Under a nitrogen atmosphere, they are calcined at 300℃ and 900℃ for 1h respectively.

[0015] Another technical solution of the present invention is: an application of a single-atom catalyst for electrocatalytic carbon dioxide reduction, characterized in that: the electrocatalytic material Applied to electrocatalytic CO2 reduction to produce CO.

[0016] Furthermore, electrocatalytic materials Applied to electrocatalytic CO2 reduction to produce CO, specifically:

[0017] The material has a ZnN5 configuration. During the reaction process, the metal Zn continuously forms and breaks bonds with pyridinic nitrogen and pyrrolic nitrogen, i.e., the vibration and pulling of the intermediate Zn metal, thereby exposing two types of nitrogen active sites (pyridinic nitrogen and pyrrolic nitrogen). At -0.67V~-1.07V vs.RHE, its carbon monoxide Faraday efficiency (FE CO )>90%; at -0.77V and -0.87V (vs.RHE), the carbon monoxide Faradaic efficiency is close to 100%, showing excellent eCO2RR performance.

[0018] Furthermore, both pyridinic nitrogen and pyrrolic nitrogen are beneficial to the formation of the reaction intermediate *COOH, while effectively utilizing *H and avoiding the unfavorable competitive reaction, namely the hydrogen evolution reaction. The key factors for achieving high selectivity and high activity are an electrocatalyst with excellent electrocatalytic CO2 reduction performance, which exhibits excellent conversion efficiency and CO product selectivity. These characteristics help single-atom catalysts in the electrocatalytic CO2 reduction process move closer to green, safe, simple and convenient industrial production.

[0019] Furthermore, the electrocatalytic reduction of CO2 to produce CO is carried out in a typical gas-tight H-type electrolytic cell. The system adopts a three-electrode system, including a working electrode, a reference electrode and a counter electrode, wherein the working electrode is a loading electrode. The carbon cloth is used as the reference electrode, the Ag / AgCl electrode is used as the counter electrode, and the carbon rod is used as the counter electrode. In this electrolytic cell, the working electrode and the reference electrode are placed in the cathode chamber, while the counter electrode is placed in the anode chamber, and the cathode chamber and the anode chamber are separated by a proton exchange membrane.

[0020] Furthermore, the working electrode was prepared by: first taking 470 μl of anhydrous ethanol and 30 μl of Nafion membrane solution to prepare a solution, and then adding 5 mg of the prepared The powder was dispersed in the solution and ultrasonically dispersed for 30 minutes to obtain a uniformly dispersed solution; 50 microliters of the dispersed solution was drop-coated on both sides of the carbon cloth and naturally dried to obtain a working electrode.

[0021] Furthermore, the operating conditions are as follows: 25 mL of 0.5 mol / L KHCO₃ solution was added to each chamber of the H-type electrolytic cell. The working electrode, reference electrode, and counter electrode were all connected to an electrochemical workstation (model CHI 660E). CO₂ gas was then introduced at a flow rate of 50 mL / min for at least 30 minutes to saturate the electrolyte. Constant-potential electrolysis was then performed at a negative potential of -1.5 V until the charge reached 5 C. During this process, gaseous and liquid products were collected.

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

[0023] (1) The electrocatalytic carbon dioxide reduction material of the present invention is a ZnN5 configuration that has never been reported. Unlike conventional metal-centered catalysts, the catalytic active center of the present catalyst is a nitrogen atom coordinated with Zn. At the same time, during the reaction, the ZnN5 configuration is in a vibration state, that is, the metal Zn continuously forms and breaks bonds with pyridinic nitrogen and pyrrolic nitrogen, thereby exposing the N active site.

[0024] (2) The multi-walled carbon nanotubes introduced in the present invention have good electrical conductivity. In addition, the introduction of g-C3N4 increases the nitrogen content on the multi-walled carbon nanotubes, which is beneficial for anchoring the metal, thereby enhancing the carbon dioxide reactivity of the reducing material.

[0025] (3) The electrocatalytic carbon dioxide reduction material provided by the present invention is low-priced, green and safe, and has a simple and convenient production process, which is of great significance for the industrial application of electrocatalytic carbon dioxide reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Single-atom catalysts Schematic diagram of the microscopic morphology. 1(a) is a scanning electron microscope image of the material, 1(b) is a transmission electron microscope image of the material, and 1(c) is a spherical aberration electron microscope image of the material.

[0027] Figure 2 Single-atom catalyst Schematic diagram of synchrotron radiation. 2(a) confirms that the material is single-atom, and 2(b) confirms that the material is ZnN5 structure.

[0028] Figure 3 Schematic diagram of the N content and Zn content of XPS of different catalyst materials.

[0029] Figure 4 Figure 2 shows the CO Faraday efficiency of different catalyst materials in an H-type electrolytic cell at different potentials (relative to RHE). DETAILED DESCRIPTION

[0030] The present invention provides a single-atom catalyst for electrocatalytic carbon dioxide reduction and a preparation method thereof. The method mainly uses g-C3N4 as a nitrogen source, Zn powder as a metal source, and multi-walled carbon nanotubes as a substrate. A high-density new configuration, namely a pentacoordinated Zn-based single-atom catalyst, is designed and synthesized by a calcination method. Unlike the common metal-N4 configuration (where the metal and four nitrogen atoms are coplanar), in the novel ZnN5 configuration, the Zn atom is pulled by the axial pyrrolic N and is located within the concave surface of the four pyridinic N atoms, weakening the metal Zn's ability to bind to CO2 as an active site. Throughout the CO2 reduction reaction, ZnN5 exhibits a special state of structural vibration, where the metal Zn continuously forms and breaks bonds with the pyridinic and pyrrolic N atoms, exposing the N active site and thus realizing this novel single-atom catalyst configuration. high selectivity and activity.

[0031] The present invention will be further described in detail below through specific embodiments, but the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] Combine Figure 1 (a) and 1(b) show an electrocatalytic material for electrocatalytic carbon dioxide reduction reaction The material is based on MWCNTs, and g-C3N4 is used to supplement the nitrogen content of MWCNTs to anchor metal zinc.

[0034] Preparation method: 10-15g of urea is placed in a crucible and then calcined in a muffle furnace at a heating rate of 5°C / min from room temperature to 550°C, held at 550°C for 4 hours, and then cooled naturally to obtain g-C3N4. While stirring, 25-30mg of g-C3N4 and 25-30mg of MWCNTs are added to 50mL of ultrapure water to form a mixed suspension. The suspension is then sonicated for 1 hour to exfoliate the g-C3N4. The gray-black suspension is then stirred for 12 hours to uniformly mix the g-C3N4 and MWCNTs. The product is then filtered, washed three times with ultrapure water, and dried overnight at 60°C to obtain a gray-black powder of MWCNTs / g-C3N4. Finally, the MWCNTs / g-C3N4 are ground with zinc powder. The mass ratio of MWCNTs / g-C3N4 to zinc powder is 2:1, and the specific mass is 45-50mg MWCNTs / g-C3N4 and 25-30mg zinc powder. The obtained gray-black powder is then placed on a porcelain boat and placed in a tubular furnace for calcination under the following conditions: the whole process heating rate is 5°C / min, first from room temperature to 60°C with nitrogen for 30min to remove air, then from 60°C to 300°C and kept at 300°C for 1h, then from 300°C to 900°C and kept at 900°C for 1h and then cooled naturally. The N2 flow rate during the whole process is controlled at 500mL / min, and the target product is finally obtained.

[0035] In this embodiment, the microscopic morphology of the material was characterized and analyzed using a scanning electron microscope, a transmission electron microscope, and a spherical aberration electron microscope. Figure 1 (a) It can be seen that the material is mainly composed of carbon nanotubes. Figure 1 (b) No obvious metal particles are present, but Figure 1 In (c), we can see that the material contains a large number of single atomic phase points. Figure 2 It is directly proved that the material is a single-atom catalyst with ZnN5 configuration.

[0036] Comparative Example 1

[0037] 10-15g of urea was placed in a crucible and then calcined in a muffle furnace at a heating rate of 5°C / min from room temperature to 550°C, held at 550°C for 4 hours, and then naturally cooled to obtain g-C3N4. While stirring, 25-30mg of g-C3N4 and 25-30mg of MWCNTs were added to 50mL of ultrapure water to prepare a mixed suspension. The suspension was then sonicated for 1h to exfoliate the g-C3N4, and the gray-black suspension was stirred for 12h to uniformly mix the g-C3N4 and MWCNTs. Finally, the product was filtered, washed three times with ultrapure water, and finally dried at 60°C overnight to obtain a gray-black powder of MWCNTs / g-C3N4. The obtained gray-black powder was then placed on a porcelain boat and calcined in a tube furnace. The conditions were: the whole process heating rate was 5℃ / min, first from room temperature to 60℃ with nitrogen for 30min to remove air, then from 60℃ to 300℃ and kept at 300℃ for 1h, then from 300℃ to 900℃ and kept at 900℃ for 1h and then cooled naturally. The N2 flow rate during the whole process was controlled at 500mL / min, and the target product was finally obtained.

[0038] Comparative Example 2

[0039] The MWCNTs and zinc powder are ground evenly. The mass ratio of MWCNTs to zinc powder is 1:1, and the specific mass is 25-30 mg MWCNTs and 25-30 mg zinc powder. The obtained gray-black powder is then placed on a porcelain boat and placed in a tubular furnace for calcination. The conditions are: the whole process heating rate is 5 ° C / min, first from room temperature to 60 ° C and nitrogen is passed for 30 minutes to remove the air, then from 60 ° C to 300 ° C, and kept at 300 ° C for 1 hour, then from 300 ° C to 900 ° C, and kept at 900 ° C for 1 hour and then cooled naturally. The N2 flow rate during the whole process is controlled at 500 mL / min, and the target product is finally obtained.

[0040] Comparative Example 3

[0041] 25-30 mg of MWCNTs were placed on a porcelain boat and calcined in a tubular furnace under the following conditions: the temperature was raised at a rate of 5°C / min throughout the entire process, first from room temperature to 60°C with nitrogen flowing for 30 minutes to remove all air, then from 60°C to 300°C and maintained at 300°C for 1 hour, then from 300°C to 900°C and maintained at 900°C for 1 hour, and then naturally cooled. The N2 flow rate was controlled at 500 mL / min throughout the entire process, and the target product MWCNTs were finally obtained.

[0042] Figure 3 It is the N content and Zn content of XPS of different catalyst materials. and In the comparison, it can be clearly observed that due to the introduction of g-C3N4, the nitrogen content of the catalyst is significantly increased, and the single-atom metal content is also successfully anchored on the multi-walled carbon nanotubes.

[0043] Figure 4 Figure 2 shows the CO Faradaic efficiency of different catalyst materials at different potentials (relative to the RHE) in an H-type electrolytic cell. Experimental parameters: Constant-potential electrolysis was performed at starting potentials ranging from -1.2 to -1.8 V, and the charge was maintained at 5 C. Before each electrolysis run, CO2 was introduced for at least 30 minutes to saturate the 0.5 mol / L KHCO3 electrolyte solution. The gas flow rate was 50 mL / min.

[0044] Figure 4 It can be seen that the The Faradaic efficiency is higher than other comparison samples, reaching 99.9% at -0.87V (vs. RHE) and is consistent across the entire voltage test range. The CO Faradaic efficiency is above 80%. The above data show that the catalyst material of the present invention has excellent catalytic activity.

[0045] The above description is merely an embodiment of the present invention. Common knowledge regarding the specific structure and characteristics of the solution is not described in detail herein. It should be noted that those skilled in the art may make various modifications and improvements without departing from the structure of the present invention, and these modifications and improvements should be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practical application of the patent.

Claims

1. A single-atom catalyst for electrocatalytic carbon dioxide reduction, characterized by: The single-atom catalyst is the electrocatalytic material MWCNTs©ZnN5. MWCNTs©ZnN5 includes MWCNTs as the conductive body, and g-C3N4 is used to supplement the nitrogen content of MWCNTs as a nitrogen source for anchoring metallic zinc; a high-density five-coordinate new configuration Zn-based single-atom catalyst is designed and synthesized on multi-walled carbon nanotubes, and the ZnN5 configuration is in a vibration state during the CO2 reduction reaction.

2. The single-atom catalyst for electrocatalytic carbon dioxide reduction according to claim 1, characterized in that: MWCNTs©ZnN5 is composed of Zn atoms containing four pyridinic nitrogen atoms in the same plane and one pyrrolic nitrogen atoms in the axial direction. The larger atomic radius of Zn atoms and the traction of Zn atoms by the axial pyrrolic nitrogen atoms make them located in the concave surface of the four pyridinic nitrogen atoms.

3. The single-atom catalyst for electrocatalytic carbon dioxide reduction according to claim 1, characterized in that: The MWCNTs©ZnN5 was tested by ICP, and the metal content in the MWCNTs©ZnN5 reached 0.54 wt%. The MWCNTs©ZnN5 showed high-density single atoms under a spherical aberration electron microscope.

4. The single-atom catalyst for electrocatalytic carbon dioxide reduction according to claim 1, characterized in that: The ZnN5 configuration is in a vibrating state during the CO2 reduction reaction. Specifically, the Zn atom in the ZnN5 configuration is located in a concave surface coplanar with four pyridinic N atoms, weakening the function of the Zn atom as an active site to bind to CO2. During the entire CO2RR reaction, ZnN5 presents a special state of structural vibration. In this special state, the metal Zn continuously forms and breaks bonds with pyridinic nitrogen and pyrrolic nitrogen, exposing the N active site and realizing the transfer of the active site from the metal center to the coordination atom in the single-atom catalyst.

5. A method for preparing a single-atom catalyst for electrocatalytic carbon dioxide reduction according to claim 1, characterized in that: (1) A certain amount of g-C3N4 was synthesized in advance, and then g-C3N4 and MWCNTs were added to the aqueous solution to obtain MWCNTs / g-C3N4 through ultrasonication and stirring. (2) Physically grinding and mixing MWCNTs / g-C3N4 and zinc powder in a certain proportion and then calcining them to obtain the target single-atom dispersed catalyst MWCNTs©ZnN5 with ZnN5 configuration; MWCNTs / g-C3N4 and zinc powder were ground evenly in a mass ratio of 2:1 and placed in a tube furnace. They were calcined at 300°C and 900°C for 1 h respectively under a nitrogen atmosphere.

6. A use of the single-atom catalyst for electrocatalytic carbon dioxide reduction according to claim 1, wherein the electrocatalytic material MWCNTs©ZnN5 is used for electrocatalytic CO2 reduction to produce CO.

7. A use of the single-atom catalyst for electrocatalytic carbon dioxide reduction according to claim 1, wherein the electrocatalytic material MWCNTs©ZnN5 is used for electrocatalytic CO2 reduction to produce CO, specifically: MWCNTs©ZnN5 material has a ZnN5 structure. During the reaction process, the metal Zn continuously forms and breaks bonds with pyridinic and pyrrolic nitrogen, which is the vibrational pull of the intermediate Zn metal, resulting in the exposure of two types of nitrogen active sites. The carbon monoxide Faraday efficiency (FE) of MWCNTs©ZnN5 at -0.67V~-1.07V vs.RHE CO )>90%.

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