In-situ preparation method of catalysts for electrocatalytic reduction of CO2

Abstract

The present application relates to an in-situ preparation method of a catalyst for electrocatalytic reduction of CO2. By in-situ preparation of single-atom doped Cu2O nanostructures on a conductive substrate, and further modification of the nanostructures with a multi-ammonia polymer, a catalyst for electrocatalytic reduction of CO2 is obtained. The catalyst prepared by the present application has a sharp pine needle-like morphology, has a large electrochemical active area, can maintain a relatively high CO2 concentration near the catalyst during catalytic reduction of CO2, and can promote enrichment on the electrode surface, thereby improving the current density. In addition, the metal single atom can improve the selectivity of CO2 reduction to formic acid, and the multi-ammonia polymer modification can improve the hydrophobicity of the catalyst and capture more CO2 to participate in the reaction, thereby further improving the Faraday efficiency of the catalyst. The preparation method is designed to grow in-situ on different substrates, solves the problem of catalyst falling off, and can greatly improve the selectivity and conversion efficiency of the copper-based catalyst for CO2 reduction products.

Description

Technical Field

[0001] This invention relates to the field of catalytic reduction of CO2, and specifically discloses an in-situ preparation method of a catalyst for electrocatalytic reduction of CO2. Background Technology

[0002] In recent years, rapid economic growth has led to increased consumption of fossil fuels, resulting in energy shortages and excessive CO2 emissions. The "greenhouse effect" caused by increased CO2 concentrations leads to global warming, resulting in rising sea levels and threats to human health. Therefore, avoiding the catastrophic consequences of continuously increasing CO2 concentrations has become one of the most serious challenges facing society today. Many countries are making various efforts to reduce CO2 emissions. Currently, in addition to developing carbon reduction technologies, carbon negative (CCUS) technology has also received widespread attention from researchers. CCUS technology strategies mainly include CO2 capture and subsequent storage and conversion. However, large-scale deployment of CO2 storage is limited by high costs and energy consumption, making it insufficient to utilize captured CO2. Therefore, converting carbon dioxide into valuable chemical products through electrochemical methods, thereby closing the carbon dioxide cycle, is a promising approach that can help alleviate the energy and environmental crisis.

[0003] However, CO2 is a very stable linear molecule with two double bonds, each with a bond energy of 803 kJ / mol, thus exhibiting high chemical stability. The π bonds in the CO2 molecule have electrons, and carbon (C) is electrophilic, allowing it to be activated and participate in reactions under certain catalysts. In recent years, despite extensive research on catalytic CO2 reduction, catalyst design still faces significant challenges in terms of product selectivity, economic feasibility, and reducing operational limitations. Electrocatalytic reduction of CO2 can reduce it to C1 compounds such as carbon monoxide, formic acid, methanol, and methane, as well as C2 compounds such as ethylene, ethanol, ethylene glycol, acetic acid, and oxalic acid. Converting CO2 into high-value-added fuels or petrochemical feedstock substitutes for storing renewable energy (such as solar, tidal, and wind power) can fundamentally achieve CO2 consumption and utilization, representing the most effective and promising research approach for negative CO2 emission control. Among these conversion products, formic acid is a key chemical with significant industrial importance and is also a high-energy liquid fuel; therefore, the reduction of CO2 to formic acid has significant research value. However, the numerous reaction pathways in the electrocatalytic reduction of CO2 lead to low product selectivity of the catalysts. Catalysts with high selectivity for formic acid, such as Pb, Hg, Sn, Cd, and Bi, suffer from weak activity and low current density, severely hindering their industrial application. Therefore, the key challenge of this technology lies in finding low-cost, highly selective catalysts to improve the conversion of CO2 to a single substance.

[0004] In recent years, Cu-based catalysts have emerged as promising candidates for electrochemical CO2 reduction due to their high abundance in nature, low cost, and high activity. Copper oxides, compared to pure metal catalysts, offer lower costs and possess abundant defect sites, which would be more conducive to CO2 reduction and inhibit hydrogen evolution reaction. However, their low current density and low selectivity of reduction products hinder their ability to meet the demands of large-scale industrial applications. Therefore, there is an urgent need to develop methods to improve the Faraday efficiency and current density of Cu2O for CO2 reduction.

[0005] Patent CN110102312A (publication date: November 15, 2019) discloses a one-dimensional cuprous oxide / silver / zinc oxide nanorod photocatalyst, its preparation method, and its application in photocatalytic CO2 reduction to CO. The patent prepares a one-dimensional Cu2O / Ag / ZnO nanorod photocatalyst using a hydrothermal and chemical reduction method for the photocatalytic reduction of CO2 to CO. The preparation process in this patent employs a power-intensive hydrothermal method, the prepared catalyst is in powder form, the catalyst reuse process is complex, and the current density is relatively low. Furthermore, the catalyst prepared by this method requires further coating onto a substrate using a mixture of Nafion, ethanol, and the catalyst, which reduces the electron transport rate between the substrate and the catalyst and increases the risk of catalyst detachment during use.

[0006] Patent CN112708903A (publication date April 27, 2021) discloses a method for preparing cuprous oxide nanowires. This method primarily uses a copper substrate as the positive electrode, a platinum sheet or carbon rod as the negative electrode, and a potassium hydroxide or sodium hydroxide solution as the electrolyte to perform an anodic oxidation reaction to obtain copper hydroxide nanowires. The prepared copper hydroxide nanowires are then calcined at a high temperature of 400-800℃ in an inert gas atmosphere to obtain Cu2O nanowires. Although the Cu2O nanowire structure prepared by this method is grown in situ on a substrate, it can only use a copper sheet as a substrate, which limits its application. Furthermore, the high-temperature calcination method results in high energy consumption.

[0007] Patent CN113249748A (publication date: August 13, 2021) discloses a method for preparing a nitrogen-doped Cu2O electrocatalyst and its application in the electrochemical reduction of CO2. The preparation method involves placing water-soluble copper salt and urea in two separate ceramic boats, then heating them in a high-temperature furnace to 300-400°C while continuously purging with argon gas. In the CO2 reduction application, the catalyst is mixed with Nafion solution and alcohol and sprayed onto a conductive substrate. This non-in-situ conductive substrate growth method reduces electron transport between the substrate and the catalyst, resulting in lower current density and the potential for catalyst detachment during use. Furthermore, the preparation method utilizes a power-intensive tube furnace heating system, leading to significant energy consumption that requires further improvement.

[0008] The Cu2O nanostructures described in the above patents have certain advantages as electrodes in the field of electrochemistry. However, the preparation methods described in these patents all employ power-intensive hydrothermal methods or even high-temperature calcination methods, which are not conducive to the current national advocacy of low-carbon and environmentally friendly concepts. The catalysts prepared by patents CN 110102312 A and CN 113249748 A are both in powder form, requiring further mixing with costly Nafion adhesive materials before spraying onto a conductive substrate. This not only increases costs but also weakens the electron transport capability between the catalyst and the substrate compared to in-situ growth methods, and increases the risk of catalyst detachment during use. Furthermore, the selectivity of these catalysts for CO2 catalytic reduction products needs further improvement. Therefore, in the preparation of Cu2O nanomaterials, innovative catalyst design is needed to synthesize catalysts with larger specific surface areas, while utilizing doping methods to enhance the selectivity of the catalyst for specific reduction products. Therefore, considering that the multi-branched structure of polyamine polymers contains a large number of amino and alkyl groups, it not only enhances the catalyst's adsorption capacity for CO2 but also improves the catalyst's hydrophobicity, preventing hydrogen evolution reactions during the catalytic process, making it an ideal catalyst modifier. However, the design and preparation of such catalysts have not yet been reported. Summary of the Invention

[0009] The purpose of this invention is to provide an in-situ preparation method for a catalyst for the electrocatalytic reduction of CO2. First, single-atom-doped nanostructured Cu2O is prepared in situ on a conductive substrate. Then, an aminosilane coupling agent is loaded onto it, followed by an amidation reaction with a star-shaped pyrimidine polymer synthesized via Michael addition. This process results in a high-performance catalyst material. Based on catalyst morphology and doping control design, this invention prepares pine needle-like single-atom-doped Cu2O in situ on a substrate, exhibiting high formic acid selectivity and Faradaic efficiency. Furthermore, based on molecular structure design, pyrimidine compounds are innovatively selected as raw materials to prepare star-shaped polymers. Michael addition is applied to the preparation of these star-shaped pyrimidine polymers, and the amino coupling agent is simultaneously amidated with the star-shaped pyrimidine polymer to achieve a tight bond with Cu2O and a significant improvement in catalytic efficiency. This yields a catalyst modified with a unique multi-branched molecular structure, ensuring a large number of adsorbed groups distributed in multiple dimensions and improving the efficiency from a spatial configuration perspective. This enriches the application of polyamine polymer molecular structure design in the field of CO2 catalysts. The CO2 reduction catalyst prepared by this method differs from traditional catalysts. Its multi-branched molecular structure exhibits more three-dimensional and efficient CO2 adsorption capacity and hydrophobicity, effectively inhibiting the hydrogen evolution reaction. Furthermore, the combination with a silane coupling agent ensures a strong bond between the polymer and the catalyst, resulting in extremely high stability and superior catalytic performance. Moreover, the preparation process of this catalyst has advantages such as low energy consumption and simple, easily controllable operation, demonstrating broad development prospects.

[0010] This invention provides an in-situ preparation method for a catalyst for the electrocatalytic reduction of CO2. The method involves first preparing a single-atom-doped nanostructured Cu2O in situ on a conductive substrate, then loading an aminosilane coupling agent, and finally reacting it with a self-made star-shaped pyrimidine polymer via an amidation reaction. The conditions and steps for preparing the catalyst are as follows:

[0011] (1) Cu2O growth on a conductive substrate: First, copper salt is dissolved in deionized water, then organic acid and cationic surfactant are added. The pH of the solution is adjusted to 11-13 using a pH adjuster. The solution is then poured into a glass electrolytic cell as the electrolyte. The conductive substrate is used as the working electrode. The electrolyte is heated to 50-80℃. The working electrode and the counter electrode are connected, and an application of 0.5-3 mA / cm is applied. 2 At a current density of 0.5-2 hours, the conductive substrate is removed, rinsed with rinsing solution, and then vacuum dried at 45-80℃ for 8-24 hours to obtain a Cu2O-loaded substrate.

[0012] (2) Cu2O loaded with single-atom metal: Alkali salt and soluble metal precursor salt are dissolved in deionized water as electrolyte. A three-electrode system is used, with the counter electrode and reference electrode connected and the Cu2O loaded substrate obtained in step (1) as the working electrode. Cyclic voltammetry is used, with voltage (relative to the reversible hydrogen electrode) ranging from -0.7 to -0.1V and 0-0.5V respectively. The scanning speed is 5-50mV / s for 20-50 cycles. The Cu2O loaded substrate is taken out, rinsed with rinsing solution and placed at room temperature for 0.5-2 hours. It is then vacuum dried at 45-80℃ for 8-24 hours to obtain a Cu2O substrate loaded with single atoms.

[0013] (3) Preparation of pyrimidine polymers: Organic solvent, diaminopyrimidine compounds and alkaline salts are added to the reactor and stirred evenly. Acrylate macromonomers are added and reacted for 20-40 minutes. HCl is added dropwise and filtered. The filtrate is stirred at room temperature for 3-5 hours and then distilled, cooled, and sampled through a chromatographic column to separate the residual monomers to obtain star-shaped pyrimidine polymers.

[0014] (4) Loading silane coupling agent: Add ethanol, deionized water and aminosilane coupling agent to the reactor, stir evenly, put in the Cu2O substrate with single atoms obtained in step (2), heat to 40-70℃ and stir continuously. After reacting for 8-15 hours, take out the substrate and rinse it with rinsing solution. Dry it under vacuum at 45-80℃ for 8-24 hours to obtain the substrate loaded with silane coupling agent.

[0015] (5) Composite preparation: The star-shaped pyrimidine polymer obtained in step (3) and deionized water are added to the reactor and stirred evenly. Then, a condensing agent is added to the reactor and the carboxyl group contained in the polymer is activated at 2-7℃. After 10-25 minutes, the temperature is raised to 25-40℃ and the substrate loaded with silane coupling agent obtained in step (4) is placed in the reactor. After reacting for 5-8 hours, the substrate is taken out, rinsed with rinsing solution, and vacuum dried at 45-80℃ for 8-24 hours to obtain the catalyst modified with polyamine polymer.

[0016] Wherein, the copper salt mentioned in step (1) is CuSO4·5H2O, CuCl2·2H2O, or Cu(NO3)2; the mass ratio of the deionized water to the copper salt mentioned in step (1) is 5-16:1; the organic acid mentioned in step (1) is lactic acid, citric acid, or oxalic acid; the cationic surfactant mentioned in step (1) is hexadecyltrimethylammonium bromide or hexadecyltrimethylammonium chloride; the molar ratio of the organic acid, cationic surfactant, and copper salt mentioned in step (1) is... 2-5:0.004-0.015:1; The pH adjuster mentioned in step (1) is NaOH, KOH or ammonia; The conductive substrate mentioned in step (1) is carbon cloth, carbon paper, nickel foam, nickel sheet, copper mesh, copper sheet, copper foam, titanium mesh, stainless steel, iron sheet or FTO conductive glass; The counter electrode mentioned in step (1) is platinum sheet electrode, platinum wire electrode, platinum mesh electrode, graphite electrode or glassy carbon electrode; The rinsing solution mentioned in step (1) is deionized water, tetrahydrofuran, isopropanol, acetone, diethyl ether or ethanol;

[0017] The alkaline salt in step (2) is KOH or NaOH, and the molar ratio of its amount to the copper salt in step (1) is 1-4:1; the soluble metal precursor salt in step (2) is one or more of lead nitrate, bismuth nitrate, and chromium nitrate, and the molar ratio of its amount to the copper salt in step (1) is 1250-16000:1; the mass ratio of the deionized water in step (2) to the copper salt in step (1) is 5-16:1; the counter electrode in step (2) is a platinum sheet electrode, platinum wire electrode, platinum mesh electrode, graphite electrode, or glassy carbon electrode; the reference electrode is a hydrogen electrode, calomel electrode, mercurous sulfate electrode, mercuric oxide electrode, or silver chloride electrode; the rinsing solution in step (2) is deionized water, tetrahydrofuran, isopropanol, acetone, diethyl ether, or ethanol;

[0018] The organic solvent in step (3) is ethanol or methanol; the diaminopyrimidine compound in step (3) is 2-(4,6-diaminopyrimidine-2-thio)butyric acid or [(4,6-diaminopyrimidine-2-yl)thio]acetic acid; the alkali salt in step (3) is LiOH, KOH or NaOH; the mass ratio of the organic solvent to the diaminopyrimidine compound in step (3) is 50-150:1; the acrylate macromonomer in step (3) is methoxy polyethylene glycol methacrylate or methoxy polyethylene glycol acrylate; the molar ratio of the alkali salt, acrylate macromonomer to the diaminopyrimidine compound in step (3) is 1-2:4.5-8:1; the molar ratio of the alkali salt to HCl in step (3) is 1.08-1.2:1;

[0019] The aminosilane coupling agent mentioned in step (4) is γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane or diethylenetriaminopropyltrimethoxysilane; the volume ratio of deionized water to ethanol in step (4) is 1:2-4, and the amount of aminosilane coupling agent is 0.5-1.5% of the total volume of deionized water and ethanol; the rinsing solution mentioned in step (4) is deionized water, tetrahydrofuran, isopropanol, acetone, diethyl ether or ethanol;

[0020] The condensing agent in step (5) is 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride and N-hydroxysuccinimide, and the molar ratio of the two to the star-shaped pyrimidine polymer is 0.5-6:0.5-6:1; the mass ratio of deionized water to star-shaped pyrimidine polymer in step (5) is 80-100:1; the rinsing solution in step (5) is deionized water, tetrahydrofuran, isopropanol, acetone, diethyl ether or ethanol.

[0021] The molecular structure of the polyamine polymer described in step (5) of the method of the present invention is as follows:

[0022]

[0023] Wherein, R1 is hydrogen or ethyl; R2 is hydrogen or methyl;

[0024] Where x, y, and n are integers representing the number of repeating units in each part of the polymer, with x ranging from 1 to 21, y ranging from 0 to 2, and n ranging from 1 to 100.

[0025] The method of the present invention has the following advantages compared with the prior art:

[0026] 1. From the perspective of molecular groups, the -OH groups on the main chain of the polyamine polymer synthesized in this invention can condense with the -OH groups on the catalyst surface to form -O-, thus allowing the polymer to be tightly bound to the catalyst via covalent bonds, reducing the risk of detachment. Simultaneously, the abundant amino groups in the polymer can, on the one hand, increase the local concentration of CO2 or carbonate molecules on the electrode surface, thereby helping the catalyst capture more CO2; on the other hand, it can increase the pH value of the solution near the catalyst, which helps stabilize intermediates in the CO2RR process and improves current density and product selectivity. Specifically, the aminosilane coupling agent provides the -OH groups in the polyamine polymer, enabling the linking of the catalyst and the pyrimidine polymer, and also provides a large number of amino groups. The heterocyclic structure of the diaminopyrimidine compound provides feasibility for multi-branched structure design and also increases the number of amino groups. The hydrophobic and hydrophilic groups in the acrylate macromonomers enhance the water solubility of the polymer while also increasing the hydrophobicity of the catalyst.

[0027] 2. From a molecular structure perspective, the polymer synthesized in this invention possesses a unique multi-branched molecular structure with heterocyclic compounds as its core. This ensures the multi-dimensional arrangement of a large number of polymers and improves the efficiency from a spatial configuration perspective, expanding the peripheral radiation range of the conductive substrate and enriching the application of polyamine polymer molecular structure design in the field of CO2 catalysts. Furthermore, the polymer's unique multi-branched molecular structure exhibits a spatial amplification effect on its hydrophobic and hydrophilic groups, enhancing water solubility while also increasing the catalyst's spatial hydrophobicity. This is beneficial for compatibility within the system and effectively prevents water penetration during CO2 reduction, thus inhibiting the hydrogen evolution reaction.

[0028] 3. From the perspective of catalyst morphology, this invention synthesizes a metal oxide catalyst with a pine needle-like structure through morphology control design, which has a more stable structure and performance. The metal oxide has a sharp needle-like structure, which can provide a large electrochemical active area, promote the enrichment of CO2 molecules on the catalyst surface during the electrocatalytic reduction reaction, and improve the reduction conversion rate. In addition, the pine needle-like catalyst structure can also maintain a relatively high local CO2 concentration near the catalyst tip in the electrolyte, thereby continuously and effectively reducing CO2, while also inhibiting the competitive hydrogen evolution reaction, thus comprehensively improving the Faraday efficiency.

[0029] 4. From the perspective of the selectivity of the catalyst for CO2 reduction products, this invention further optimizes the above-mentioned pine needle-like metal oxide structure by doping it with metal single atoms that are conducive to the formation of formic acid. The single atoms are isolated and dispersed on the pine needle-like metal oxide support, giving the catalyst uniform, independent, and spatially separated active sites. Therefore, CO2 adsorbed on the catalyst surface is more likely to form HCOO. * This facilitates the formation of formic acid, maximizing the advantages of high selectivity and high reaction efficiency of hydrogen evolution-inhibiting metals in CO2 reduction, thereby improving the catalytic activity and selectivity of the catalyst for CO2 catalytic reaction.

[0030] 5. From the perspective of catalyst preparation process, unlike traditional catalysts that are bonded to conductive substrates via Nafion bonding, the catalyst prepared in this invention is grown directly in situ on the conductive substrate through electrochemical deposition. This method achieves a tight bond between the catalyst and the conductive substrate, thereby accelerating electron transport and increasing current density. It also avoids problems such as catalyst shedding and agglomeration during use, thus improving catalyst durability. Furthermore, this invention innovatively applies the Michael addition reaction to the preparation of catalyst-modified polymers. The entire preparation process avoids high temperature and high pressure conditions, making it more energy-efficient and controllable.

[0031] Therefore, this invention not only provides a novel type of catalyst for the efficient conversion and utilization of CO2 to prepare high-value-added chemicals, but also provides a method for synthesizing polyamine polymers to improve the reduction performance of the catalyst. This invention not only provides a simple and reliable preparation method for morphology control of pine needle-like Cu-based oxides, but also offers new ideas for the design and preparation of polyamine polymer-modified catalysts, showing broad application prospects in the field of catalytic reduction of CO2 catalysts. Attached Figure Description

[0032] Figure 1 Scanning electron microscope image of Example 1

[0033] Figure 2 Example 2 Scanning electron microscope image

[0034] Figure 3 Example 3 Scanning electron microscope image

[0035] Figure 4 Example 1: High-angle annular dark-field scanning transmission electron microscope image

[0036] Figure 5 Example 2: High-angle annular dark-field scanning transmission electron microscope image

[0037] Figure 6 Example 3: High-angle annular dark-field scanning transmission electron microscope image

[0038] Figure 7 Linear sweep current-voltage curve (LSV) plot

[0039] Figure 8 Comparative Example 1: Double-layer Capacitor

[0040] Figure 9 Comparative Example 2: Double-layer Capacitor

[0041] Figure 10 Example 1: Double-layer capacitor

[0042] Figure 11 Example 2: Double-layer capacitor

[0043] Figure 12 Example 3: Double-layer capacitor

[0044] Figure 13 Faraday efficiency of each sample at -0.9V

[0045] Figure 14 Faraday efficiency of Example 1 under different voltages

[0046] Figure 15 Example 2 Faraday efficiency under different voltages

[0047] Figure 16 Faraday efficiency in Example 3 under different voltages Detailed Implementation

[0048] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0049] Example 1:

[0050] (1) First, dissolve 7.50g CuSO4·5H2O in 100ml deionized water, then add 5.40g lactic acid and 0.04g hexadecyltrimethylammonium bromide. Adjust the pH of the solution to 11 with NaOH granules, pour it into a glass electrolytic cell as the electrolyte, and then add 4cm... 2 A carbon paper substrate is used as the working electrode, and a platinum sheet is used as the counter electrode. The electrode is heated to 50°C, and the working and counter electrodes are connected. An application of 2 mA / cm² is applied. 2 The current density was measured, and the conductive substrate was removed after 1 hour of deposition. It was rinsed with deionized water and vacuum dried at 45°C for 8 hours to obtain a Cu2O loaded substrate.

[0051] (2) Dissolve 6.73g KOH and 1.66mg lead nitrate in 100ml deionized water as electrolyte. Use a three-electrode system. Use the Cu2O substrate loaded in step (1) as the working electrode, the platinum electrode as the counter electrode, and Ag / AgCl as the reference electrode. Scan 20 cycles at a scanning voltage of -0.5-0.2V and a scanning speed of 10mV / S. Take out the Cu2O substrate, rinse it with deionized water and place it at room temperature for 1.5 hours. Then, vacuum dry it at 45℃ for 8 hours to obtain a Cu2O substrate loaded with single atoms.

[0052] (3) Add 100 ml of anhydrous ethanol, 0.80 g of [(4,6-diaminopyrimidin-2-yl)thio]acetic acid and 0.09 g of LiOH to the reactor and stir until homogeneous. Add 12.00 g of methoxy polyethylene glycol methacrylate with a molecular weight of 600. After reacting for 20 minutes, add 0.44 g of 37.5% hydrochloric acid dropwise. Filter the solution. After stirring the filtrate at room temperature for 3 hours, distill the filtrate, cool it, and add it to a chromatographic column to separate the residual monomers, obtaining a star-shaped pyrimidine polymer.

[0053] (4) Add 30 ml of anhydrous ethanol, 10 ml of deionized water and 0.4 ml of γ-aminopropyltriethoxysilane to the reactor, stir evenly, put in the Cu2O substrate loaded with single atoms obtained in step (2), heat to 50°C and stir continuously. After reacting for 10 hours, take out the substrate, rinse with anhydrous ethanol, and vacuum dry at 45°C for 8 hours to obtain the substrate loaded with silane coupling agent.

[0054] (5) Add 1.56g of star-shaped pyrimidine polymer obtained in step (3) and 150ml of deionized water to the reactor and stir evenly. Then add 0.22g of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride and 0.14g of N-hydroxysuccinimide to the reactor. Activate the carboxyl groups contained in the polymer at 2℃. After 15 minutes, raise the temperature to 30℃ and place the substrate loaded with silane coupling agent obtained in step (4). After reacting for 6 hours, take it out, rinse with anhydrous ethanol, and vacuum dry at 45℃ for 10 hours to obtain the catalyst modified with polyamine polymer.

[0055] Example 2:

[0056] (1) First, dissolve 8.52g CuCl2·2H2O in 100ml deionized water, then add 19.21g citric acid and 0.11g hexadecyltrimethylammonium bromide. Adjust the pH of the solution to 11.5 with NaOH granules, pour it into a glass electrolytic cell as the electrolyte, and then add 4cm... 2 A carbon cloth substrate was used as the working electrode, and glassy carbon was used as the counter electrode. The electrode was heated to 50°C, and the working and counter electrodes were connected. An application of 1.5 mA / cm² was applied. 2 The current density was measured, and the conductive substrate was removed after 0.8 hours of deposition. It was then rinsed with deionized water and vacuum dried at 45°C for 8 hours to obtain a Cu2O-loaded substrate.

[0057] (2) Dissolve 4.00g KOH and 4.85mg bismuth nitrate in 100ml deionized water as electrolyte. Use a three-electrode system. Use the Cu2O substrate loaded in step (1) as the working electrode, the platinum electrode as the counter electrode, and Ag / AgCl as the reference electrode. Scan for 40 cycles at a scanning voltage of -0.6-0.1V and a scanning speed of 15mV / S by cyclic voltammetry. Take out the Cu2O substrate, rinse it with deionized water and let it stand naturally for 2 hours. Then, vacuum dry it at 50℃ for 12 hours to obtain a Cu2O substrate loaded with single atoms.

[0058] (3) Add 150 ml of anhydrous ethanol, 2.05 g of [(4,6-diaminopyrimidine-2-yl)thio]butyric acid and 0.42 g of NaOH to the reactor and stir until homogeneous. Add 43.20 g of methoxy polyethylene glycol acrylate with a molecular weight of 600. After reacting for 30 minutes, add 1.14 g of 37.5% hydrochloric acid dropwise. Filter the solution. After stirring the filtrate at room temperature for 3 hours, distill the filtrate, cool it, and add it to a chromatographic column to separate the residual monomers, obtaining a star-shaped pyrimidine polymer.

[0059] (4) Add 60 ml of anhydrous ethanol, 20 ml of deionized water and 1 ml of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane to the reactor, stir evenly, put in the Cu2O substrate loaded with single atoms obtained in step (2), heat to 60°C and stir continuously. After reacting for 12 hours, take out the substrate, rinse with anhydrous ethanol, and vacuum dry at 50°C for 12 hours to obtain the substrate loaded with silane coupling agent.

[0060] (5) Add 2.34g of star-shaped pyrimidine polymer obtained in step (3) and 150ml of deionized water to the reactor and stir evenly. Then add 0.49g of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride and 0.31g of N-hydroxysuccinimide to the reactor. Activate the carboxyl groups contained in the polymer at 3℃. After 20 minutes, raise the temperature to 25℃ and place the substrate loaded with silane coupling agent obtained in step (4) into the reactor. After reacting for 8 hours, remove the substrate, rinse with acetone, and vacuum dry at 50℃ for 12 hours to obtain the catalyst modified with polyamine polymer.

[0061] Example 3:

[0062] (1) First, dissolve 15.00g Cu(NO3)2 in 100ml deionized water, then add 25.21g citric acid and 0.28g hexadecyltrimethylammonium chloride. Adjust the pH of the solution to 12 with KOH granules, pour it into a glass electrolytic cell as the electrolyte, and then add 6cm... 2 A carbon cloth substrate was used as the working electrode, and graphite as the counter electrode. The electrode was heated to 60°C, and the working and counter electrodes were connected. An application of 1.5 mA / cm² was applied. 2 The current density was measured, and the conductive substrate was removed after 1.5 hours of deposition. It was then rinsed with deionized water and vacuum dried at 60°C for 12 hours to obtain a Cu2O-loaded substrate.

[0063] (2) Dissolve 3.20g KOH and 4.76mg chromium nitrate in 100ml deionized water as electrolyte. Use a three-electrode system. Use the Cu2O substrate loaded in step (1) as the working electrode, the platinum electrode as the counter electrode, and Ag / AgCl as the reference electrode. Scan 60 cycles at a scanning voltage of -0.3-0.3V and a scanning speed of 20mV / S by cyclic voltammetry. Take out the Cu2O substrate, rinse it with deionized water and place it at room temperature for 2.5 hours. Then vacuum dry it at 60℃ for 12 hours to obtain a Cu2O substrate loaded with single atoms.

[0064] (3) Add 200 ml of anhydrous ethanol, 3.20 g of [(4,6-diaminopyrimidine-2-yl)thio]butyric acid and 0.91 g of KOH to the reactor and stir until homogeneous. Add 57.60 g of methoxy polyethylene glycol methacrylate with a molecular weight of 600. After reacting for 30 minutes, add 1.65 g of 37.5% hydrochloric acid dropwise. Filter the solution. After stirring the filtrate at room temperature for 3 hours, distill the filtrate, cool it, and add it to a chromatographic column to separate the residual monomers, obtaining a star-shaped pyrimidine polymer.

[0065] (4) Add 70 ml of anhydrous ethanol, 30 ml of deionized water and 1.5 ml of diethylenetriaminepropyltrimethoxysilane to the reactor, stir evenly, put in the Cu2O substrate loaded with single atoms obtained in step (2), heat to 60°C and stir continuously. After reacting for 12 hours, take out the substrate, rinse with anhydrous ethanol, and vacuum dry at 50°C for 12 hours to obtain the substrate loaded with silane coupling agent.

[0066] (5) Add 4.16g of star-shaped pyrimidine polymer obtained in step (3) and 200ml of deionized water to the reactor and stir evenly. Then add 1.15g of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride and 0.73g of N-hydroxysuccinimide to the reactor. Activate the carboxyl groups contained in the polymer at 3℃. After 20 minutes, raise the temperature to 25℃ and place the substrate loaded with silane coupling agent obtained in step (4) into the reactor. After reacting for 8 hours, take it out, rinse with deionized water, and vacuum dry at 50℃ for 12 hours to obtain the catalyst modified with polyamine polymer.

[0067] Implementation results:

[0068] 1. Microscopic morphological characterization

[0069] In the above embodiments, a three-dimensional Cu2O nanostructure with a pine needle-like morphology was prepared. The morphology of the sample and the loaded single atoms were observed using scanning electron microscopy and high-angle annular dark-field scanning transmission electron microscopy. Figures 1-3 Scanning electron microscope (SEM) images of the catalysts prepared in Examples 1, 2, and 3, respectively. Figures 4-6 The images shown are high-angle annular dark-field scanning transmission electron microscope (STEM) images of the catalysts prepared in Examples 1, 2, and 3, respectively.

[0070] From scanning electron microscopy Figures 1-3 As can be seen, the catalysts prepared in the three examples all exhibit a randomly arranged, pine needle-like morphology with sharp tips and a length of 2-4 μm. (This information was obtained from a high-angle annular dark-field scanning electron microscope.) Figures 4-6 It can be clearly seen that the bright spots are doped single atoms, with atomically dispersed metal single atoms dispersed in the catalyst.

[0071] 2. Electrochemical performance of the catalyst:

[0072] A three-electrode system was used in an H-type two-chamber electrolytic cell containing 0.5 M KHCO3 electrolyte. The two chambers of the H-type electrochemical cell were separated using a Nafion 117 membrane, and 30 ml of the solution was added to each of the two chambers. A 1 cm² area... 2 The catalyst was used as the working electrode, the Ag / AgCl electrode as the reference electrode was placed in the cathode electrolysis chamber, and the platinum sheet electrode was placed in the anode chamber as the counter electrode. Before electrolysis began, high-purity CO2 gas at a flow rate of 20 ml / min was continuously introduced into the cathode chamber for 30 minutes to ensure CO2 saturation in the KHCO3 solution, during which the current density was automatically compensated for by 80% iR. Figure 7 Linear sweep voltammetry (LSV) curves of Examples 1, 2, and 3, and Comparative Examples 1 and 2. Comparative Example 1 is a Cu₂O thin film prepared on carbon paper, using the same preparation method as step (1) of Example 1, but without the addition of a cationic surfactant. Comparative Example 2 is a pine needle-shaped Cu₂O catalyst supported on carbon paper, prepared using the same method as steps (1) and (2) of Example 1. During testing, the potential range was selected as -1.0 to 0.2 V (relative to the reversible hydrogen electrode).

[0073] Figure 7 The results show that as the scanning potential shifts in the negative direction, the current density of the sample increases rapidly. Examples 1, 2, and 3 all exhibited higher current densities compared to the comparative examples, with Example 1 showing the best performance. Example 1 had an open-circuit voltage of -0.25V, lower than the other two examples and the comparative examples. Comparison of Comparative Example 1 with other catalysts reveals that the pine needle-like morphology and single-atom doping significantly improved the catalyst's current density. Furthermore, the comparison between Comparative Example 2 and the examples demonstrates that the catalyst's performance was further improved by the polyamine polymer modification, exhibiting higher electrocatalytic activity.

[0074] 3. Electrochemical active area of ​​the catalyst

[0075] For the electrochemical applications of nanomaterials, an important parameter is the electrochemical active area of ​​the catalyst. Therefore, the electrochemical catalytic performance of the catalyst is evaluated by measuring and calculating its electrochemical active area. This invention uses the cyclic voltammetry method to determine the double-layer capacitance. The specific operation is as follows: In an H-type two-chamber electrolytic cell containing 0.5M KHCO3 electrolyte, the two chambers of the H-type electrochemical cell are separated using a Nafion 117 membrane. 30ml of the solution is added to each of the two electrolytic cell chambers; a 1cm² active area is then used to measure the active area of ​​the catalyst. 2The catalyst was used as the working electrode, the Ag / AgCl electrode was used as the reference electrode and placed in the cathode electrolysis chamber, and the platinum sheet electrode was used as the counter electrode and placed in the anode chamber. Before the electrolysis started, high-purity CO2 gas at a flow rate of 20 ml / min was continuously introduced into the cathode chamber for 30 minutes to ensure that the KHCO3 solution was saturated with CO2. The curves of different scan rates were measured by cyclic voltammetry, and then the current density and scan rate at the same potential were plotted to obtain the double-layer capacitance diagram. Figures 8-12 The images show the double-layer capacitance diagrams for Comparative Example 1, Comparative Example 2, Example 1, Example 2, and Example 3, respectively. The electrochemical active area of ​​the samples can be obtained by comparing the double-layer capacitance value with the ideal capacitance value of a smooth Cu2O surface.

[0076] From the above figures, it can be seen that the electrochemical active areas of Comparative Example 1, Comparative Example 2, Example 1, Example 2, and Example 3 are respectively 35 cm². 2 102cm 2 137cm 2 120cm 2 115cm 2 Therefore, it can be seen that the electrochemical active surface areas of Examples 1-3 are all larger than those of the comparative example, with Example 1 exhibiting the largest electrochemical active surface area, which is attributed to its superior electrochemical active surface area. The larger electrochemical active surface area of ​​Example 1 is due to the unique morphology and structure of the catalyst and the contribution of active sites within the catalyst, which is beneficial for accelerating the electrochemical catalytic reduction of CO2.

[0077] 4. Effect of catalyst on CO2 electroreduction

[0078] A three-electrode system was used in an H-type two-chamber electrolytic cell containing 0.5 M KHCO3 electrolyte. The two chambers of the H-type electrochemical cell were separated using a Nafion 117 membrane, and 30 ml of the solution was added to each of the two chambers. A 1 cm² area... 2 A catalyst was used as the working electrode, an Ag / AgCl electrode as the reference electrode in the cathode electrolysis chamber, and a platinum sheet electrode as the counter electrode in the anode chamber. Before electrolysis began, high-purity CO2 gas at a flow rate of 20 ml / min was continuously introduced into the cathode chamber for 30 minutes to ensure CO2 saturation in the KHCO3 solution. A voltage of -0.9 V was applied to the working electrode for 2 hours of electrolysis. After 20 minutes of electrolysis, the gas was collected using a gas collecting bag, and after 2 hours of electrolysis, the liquid was collected and analyzed using nuclear magnetic resonance (NMR). 1 Quantitative characterization and determination were performed using H-spectrum.

[0079] Figure 13The figure shows the Faraday efficiency of the comparative and examples at a voltage of -0.9V. It can be seen from the figure that the selectivity of the catalyst for formic acid increased by 2.6 times after doping with a single atom, while the hydrogen evolution efficiency of the catalyst decreased. Moreover, the formic acid selectivity and Faraday efficiency of the catalyst modified with polyamine polymer increased by 3.4-3.5 times compared with comparative example 1, and by 19.35%-22.97% compared with comparative example 2. Among them, example 1 is the best. Figures 14-16 The figures show the CO2 conversion efficiencies of Examples 1, 2, and 3 at different voltages. As can be seen from the figures, the formic acid selectivity is the highest at -0.9V, with Example 1 exhibiting the best formic acid selectivity and the highest Faraday efficiency.

Claims

1. A method for in-situ preparation of a catalyst for the electrocatalytic reduction of CO2, characterized in that, The conditions and steps for preparing a catalyst by first preparing single-atom-doped Cu2O nanostructures in situ on a conductive substrate, then loading an aminosilane coupling agent, and finally reacting it with a self-made star-shaped pyrimidine polymer via an amidation reaction are as follows: (1) Cu2O growth on a conductive substrate: First, copper salt is dissolved in deionized water, then organic acid and cationic surfactant are added. The pH of the solution is adjusted to 11-13 using a pH adjuster. The solution is then poured into a glass electrolytic cell as the electrolyte. The conductive substrate is used as the working electrode. The electrolyte is heated to 50-80℃. The working electrode and the counter electrode are connected, and an application of 0.5-3 mA / cm is applied. 2 At a current density of 0.5-2 hours, the conductive substrate is removed, rinsed with rinsing solution, and then vacuum dried at 45-80℃ for 8-24 hours to obtain a Cu2O-loaded substrate. (2) Cu2O loaded with single-atom metal: Alkali salt and soluble metal precursor salt are dissolved in deionized water as electrolyte. A three-electrode system is used, connecting the counter electrode and the reference electrode, and the Cu2O loaded substrate obtained in step (1) is used as the working electrode. Cyclic voltammetry is used, with the voltage range relative to the reversible hydrogen electrode being between -0.7 and -0.1V and between 0 and 0.5V. The scan is performed at a scan rate of 5-50mV / s for 20-50 cycles. The Cu2O loaded substrate is taken out, rinsed with rinsing solution and placed at room temperature for 0.5-2 hours. It is then vacuum dried at 45-80℃ for 8-24 hours to obtain a Cu2O substrate loaded with single atoms. (3) Preparation of pyrimidine polymer: Add organic solvent, diaminopyrimidine compound and alkaline salt to reactor, stir evenly, add acrylate macromonomer, react for 20-40 minutes, add HCl dropwise, filter, stir the filtrate at room temperature for 3-5 hours, distill the filtrate, cool, add sample and separate residual monomer through chromatographic column to obtain star-shaped pyrimidine polymer; (4) Loading silane coupling agent: Add ethanol, deionized water and aminosilane coupling agent to the reactor, stir evenly, put in the Cu2O substrate loaded with single atoms obtained in step (2), heat to 40-70℃ and stir continuously. After reacting for 8-15 hours, take out the substrate and rinse it with rinsing solution. Dry it under vacuum at 45-80℃ for 8-24 hours to obtain the substrate loaded with silane coupling agent. (5) Composite preparation: The star-shaped pyrimidine polymer obtained in step (3) and deionized water are added to the reactor and stirred evenly. Then, a condensing agent is added to the reactor and the carboxyl group contained in the polymer is activated at 2-7℃. After 10-25 minutes, the temperature is raised to 25-40℃ and the substrate loaded with silane coupling agent obtained in step (4) is placed in the reactor. After reacting for 5-8 hours, the substrate is taken out, rinsed with rinsing solution, and vacuum dried at 45-80℃ for 8-24 hours to obtain the catalyst modified with polyamine polymer. Wherein, the copper salt mentioned in step (1) is CuSO4·5H2O, CuCl2·2H2O, or Cu(NO3)2; the mass ratio of the deionized water mentioned in step (1) to the copper salt mentioned in step (1) is 5-16:1; the organic acid mentioned in step (1) is lactic acid, citric acid, or oxalic acid; the cationic surfactant mentioned in step (1) is hexadecyltrimethylammonium bromide or hexadecyltrimethylammonium chloride; the molar ratio of the organic acid, cationic surfactant, and copper salt mentioned in step (1) is... 2-5:0.004-0.015:1; The pH adjuster in step (1) is NaOH, KOH or ammonia; The conductive substrate in step (1) is carbon cloth, carbon paper, nickel foam, nickel sheet, copper mesh, copper sheet, copper foam, titanium mesh, stainless steel, iron sheet or FTO conductive glass; The counter electrode in step (1) is platinum sheet electrode, platinum wire electrode, platinum mesh electrode, graphite electrode or glassy carbon electrode; The rinsing solution in step (1) is deionized water, tetrahydrofuran, isopropanol, acetone, diethyl ether or ethanol; The alkaline salt in step (2) is KOH or NaOH, and the molar ratio of its amount to the copper salt in step (1) is 1-4:1; the soluble metal precursor salt in step (2) is one or more of lead nitrate, bismuth nitrate, and chromium nitrate, and the molar ratio of its amount to the copper salt in step (1) is 1:5000, 1:4000, or 1:6000; the mass ratio of the deionized water in step (2) to the copper salt in step (1) is 5-16:1; the counter electrode in step (2) is a platinum sheet electrode, platinum wire electrode, platinum mesh electrode, graphite electrode, or glassy carbon electrode; the reference electrode is a hydrogen electrode, calomel electrode, mercurous sulfate electrode, mercuric oxide electrode, or silver chloride electrode; the rinsing solution in step (2) is deionized water, tetrahydrofuran, isopropanol, acetone, diethyl ether, or ethanol; The organic solvent in step (3) is ethanol or methanol; the diaminopyrimidine compound in step (3) is 2-[(4,6-diaminopyrimidine-2-yl)thio)]butyric acid or 2-[(4,6-diaminopyrimidine-2-yl)thio]acetic acid; the alkali salt in step (3) is LiOH, KOH or NaOH; the mass ratio of the organic solvent to the diaminopyrimidine compound in step (3) is 50-150:1; the acrylate macromonomer in step (3) is methoxy polyethylene glycol methacrylate or methoxy polyethylene glycol acrylate; the molar ratio of the alkali salt, acrylate macromonomer to the diaminopyrimidine compound in step (3) is 1-2:4.5-8:1; the molar ratio of the alkali salt to HCl in step (3) is 1.08-1.2:1; The aminosilane coupling agent mentioned in step (4) is γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane or diethylenetriaminopropyltrimethoxysilane; the volume ratio of deionized water to ethanol in step (4) is 1:2-4, and the amount of aminosilane coupling agent is 0.5-1.5% of the total volume of deionized water and ethanol; the rinsing solution mentioned in step (4) is deionized water, tetrahydrofuran, isopropanol, acetone, diethyl ether or ethanol; The condensing agent in step (5) is 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride and N-hydroxysuccinimide, and the molar ratio of the two to the star-shaped pyrimidine polymer is 0.5-6:0.5-6:1; the mass ratio of the deionized water to the star-shaped pyrimidine polymer in step (5) is 80-100:1; the rinsing solution in step (5) is deionized water, tetrahydrofuran, isopropanol, acetone, diethyl ether or ethanol.

2. The method according to claim 1, characterized in that, The molecular structure of the polyamine polymer described in step (5) is as follows: ； Wherein, R1 is hydrogen or ethyl; R2 is hydrogen or methyl; where x, y, and n are integers representing the number of repeating units in each part of the polymer, x ranges from 1 to 21, y ranges from 0 to 2, and n ranges from 1 to 100.

Images