Carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic co2 reduction catalyst, preparation method and application thereof

Abstract

The application relates to an electrocatalytic CO2 reduction catalyst, in particular to a carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst, a preparation method and application thereof, and belongs to the technical field of electrocatalysis. The method comprises the following steps: S1, carbon nanotubes are heated at a temperature of 400-500 DEG C for 0.5-1.5 h to remove impurities contained in the carbon nanotubes; S2, the carbon nanotubes are subjected to oxidation treatment to introduce hydroxyl groups; S3, the oxidized carbon nanotubes obtained through S2 treatment are subjected to ultrasonic treatment in a solvent DMF environment to load a molecular catalyst; and S4, the oxidized carbon nanotubes loaded with the molecular catalyst in S3 are subjected to hydrophobic modification on the carbon nanotubes in a silane aqueous solution by using silane. The carbon-fluorine chain of silane with excellent hydrophobicity is stably anchored on the surface of the carbon nanotubes through a covalent bond connection strategy, so as to solve the problems that the hydrophobicity of a catalytic electrode prepared by using an existing carbon-based catalyst is easy to be lost, the catalytic performance is easy to be reduced, and the stability is not high in a reaction.

Description

TECHNICAL FIELD

[0001] The application relates to an electrocatalytic CO2 reduction catalyst, in particular to a carbon-fluorocarbon chain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst, a preparation method and application thereof, and belongs to the technical field of electrocatalysis. BACKGROUND

[0002] The consumption of fossil raw materials is increasing, which has brought about serious climate problems. The emission and utilization of CO2 have become an important topic in current scientific research and industrial application. The electrocatalytic CO2 reduction reaction (CO2RR) as a method for converting CO2 into high-value chemical raw materials or fuels by using renewable energy has received extensive attention. The electrocatalytic CO2 reduction reaction can convert CO2 into high-value chemical raw materials or fuels by using renewable energy. In order to achieve high catalytic activity and stable reaction process, it is crucial to ensure the hydrophobicity of the electrocatalytic electrode when the CO2RR is carried out at an industrial relevant current density. The hydrophobic electrode helps to improve the gas transmission of CO2 and ensures that the CO2 reactant can smoothly reach the catalytically active site.

[0003] At present, in order to explore the influence of the hydrophobic environment on the selectivity and stability of CO2RR, different hydrophobic methods are explored and optimized by research teams. Wakerley et al. published a research result entitled "Bio-inspired hydrophobicity promotes CO2 reduction on a Cu surface" in Nature Materials. A copper electrode with a hydrophobic dendritic structure is prepared. The hydrophobic surface can significantly increase the local CO2 concentration on the surface of the catalyst, and the faradic efficiency of ethylene is increased from 9% of the hydrophilic electrode to 56% of the faradic efficiency of ethylene; Chang et al. reported in the research work entitled "Ionomers Modify the Selectivity of Cu-Catalyzed Electrochemical CO2 Reduction" published in ChemSuschem that the addition of ionomer will change the hydrophilic and hydrophobic properties of the electrode, and significantly change the selectivity of the Cu catalyst. At various current densities, hydrogen is the main product of the hydrophilic Cu / PTP catalytic electrode.

[0004] Carbon-based materials are widely used in the preparation of CO2RR catalysts due to their good electrical conductivity, large specific surface area, and high chemical stability. However, conventional carbon-based materials often have poor hydrophobicity, and in the actual preparation of catalytic electrodes, additional hydrophobic materials such as PTFE particles are often added to maintain the hydrophobicity of the catalytic electrode. However, due to the possible shedding of hydrophobic materials during the reaction, the hydrophobicity of the electrode is often reduced, which affects the catalytic performance of the catalyst. SUMMARY

[0005] The present application aims to provide a carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst to solve the problems of existing carbon-based catalyst preparation, such as easy loss of hydrophobicity during reaction, easy decline of catalytic performance, and poor stability.

[0006] The technical solution adopted by the present application to solve its technical problems is:

[0007] A preparation method of a carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst, the method comprising the following steps:

[0008] S1, carbon nanotubes are heated at a temperature of 400-500℃ for 0.5-1.5h, cooled to room temperature, washed and purified by acid treatment, washed, and freeze-dried to remove impurities contained in the carbon nanotubes;

[0009] S2, the carbon nanotubes obtained by pretreatment in S1 are heated in a mixed solution of 96-98% concentrated sulfuric acid, sodium nitrate, and potassium permanganate to introduce hydroxyl groups, washed, and freeze-dried;

[0010] The oxidation treatment temperature is not higher than 45℃;

[0011] S3, the oxidized carbon nanotubes obtained by treatment in S2 are treated by ultrasonic treatment in a solvent DMF environment to load a molecular catalyst, washed, and freeze-dried;

[0012] The molecular catalyst is cobalt phthalocyanine (CoPc) or nickel phthalocyanine;

[0013] S4, the oxidized carbon nanotubes loaded with the molecular catalyst in S3 are hydrophobically modified by silane in an aqueous silane solution, heated to 45-120℃ for 2-4h, centrifuged to remove unreacted reagents, and freeze-dried to obtain a carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst (CoPc MDE-Si);

[0014] Preparation of the aqueous silane solution: the silane content is 1-10wt%, the solvent is a mixture of ethanol and water with a mass ratio of 1-2:1, and the silane is hydrolyzed for 1-6h after mixing with the solvent;

[0015] The mass ratio of the oxidized carbon nanotubes to the silane is 10:1 to 60:1.

[0016] Preferably, the mass ratio of the oxidized carbon nanotubes to the silane is 15 to 25:1. When the silane is selected from 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, the mass ratio of the oxidized carbon nanotubes to the silane is most preferably 20:1.

[0017] In the present application, the carbon nanotubes can be single-walled carbon nanotubes or multi-walled carbon nanotubes. Single-walled carbon nanotubes (SWCNTs) are formed by rolling up a single layer of graphene; multi-walled carbon nanotubes (MWCNTs) are formed by rolling up multiple layers of graphene concentrically, which are not specifically limited herein.

[0018] Preferably, the S1 acid washing step is to heat the carbon nanotubes in a 4 to 8 mol / L hydrochloric acid solution at 130 to 150°C for 2 to 3 hours. The acid washing is to remove metal impurities or other residues that can be contained in the carbon nanotubes, and the acid washing can effectively improve the purity and quality of the carbon nanotubes.

[0019] Preferably, the reaction temperature for the oxidation treatment of the carbon nanotubes to introduce hydroxyl groups in S2 is 40 to 45°C.

[0020] Preferably, the silane comprises one or more of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, 1H, 1H, 2H, 2H-perfluorododecyltrichlorosilane, (3, 3, 3-trifluoropropyl) trimethoxysilane, 1-(trimethylsilyl) heptafluoropropane, 3, 3, 3-trifluoropropylmethyl dimethoxysilane, propyl trimethoxysilane or hexadecyl trimethoxysilane. Preferably, the silane is 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane.

[0021] Preferably, in S4, the heating is sequentially performed at 40 to 50°C for 2 to 3 hours, at 70 to 80°C for 10 to 20 minutes, heated to boiling and kept for 20 to 40 minutes to promote the full grafting of the silanol groups. The optimal conditions are heating at 48°C for 2.5 hours, at 75°C for 15 minutes, heated to boiling and kept for 30 minutes.

[0022] Preferably, the oxidation treatment in S2 to introduce hydroxyl groups is as follows: the purified pretreated carbon nanotubes are stirred overnight in 96-98% concentrated sulfuric acid at room temperature; sodium nitrate is added when the solution is heated to 40-45°C; potassium permanganate is slowly added while maintaining the reaction temperature below 45°C; the ratio of carbon nanotubes: 96-98% concentrated sulfuric acid: sodium nitrate: potassium permanganate is 1g: 20ml-23ml: 280mg-420mg: 0.8g-1.2g; stirring is then continued at 40-44°C, with appropriate amounts of water added intermittently. After the reaction is fully completed, heating is stopped, and appropriate amounts of water and hydrogen peroxide are added to the system to terminate the reaction. The ratio of carbon nanotubes: 96-98% concentrated sulfuric acid: sodium nitrate: potassium permanganate is preferably 1g: 20ml-23ml: 350mg: 1g. According to the inventors' multiple experiments, the degree of oxidation of carbon nanotubes affects the amount of modified silane. The ratio of carbon nanotubes, 96-98% concentrated sulfuric acid, sodium nitrate, and potassium permanganate is very critical. Increasing the degree of oxidation can introduce more hydroxyl groups on the surface of carbon nanotubes, thereby grafting more silane groups and improving the hydrophobicity of silane-modified carbon nanotubes. However, excessive oxidation will damage the graphite structure of carbon nanotubes, reduce their conductivity and the loading capacity of molecular catalysts, thereby affecting catalytic performance.

[0023] A carbon-fluorochain-modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst according to the present invention.

[0024] A use of the carbon-fluorochain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst described in the present invention in the preparation of catalyst ink.

[0025] The present invention provides an application of the carbon-based hydrophobic electrocatalytic CO2 reduction catalyst modified with a carbon-fluorine chain in the preparation of a working electrode. The working electrode is mainly used in the field of electrocatalytic CO2 reduction to produce CO.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention firmly anchors the carbon-fluorine chain of silane with excellent hydrophobic properties on the surface of carbon nanotubes through a covalent bond connection strategy. This combination method can greatly improve the hydrophobicity of the prepared catalyst, and the hydrophobicity can still maintain a high degree of stability during the reaction. By selecting the type of grafted silane, the hydrophobicity of the hydrophobically modified carbon nanotubes is regulated; by enhancing the hydrophobicity of the catalyst surface, the present invention effectively maintains the structural stability of the three-phase interface (gas-liquid-solid) that is crucial in the catalytic process, and effectively prevents the electrolyte from invading the Wiener pore structure of the electrode, thereby avoiding the occurrence of electrode flooding due to excessive infiltration of the electrolyte.

[0028] 2、The application forms a dense and stable hydrophobic barrier on the surface of carbon nanotubes, effectively inhibits the common water flooding phenomenon in electrocatalytic process, ensures the transmission process of CO2 in the electrode during the reaction process, and reduces the mass transfer resistance of CO2. Therefore, the catalytic performance of the electrode can be effectively improved, the reaction current density is significantly increased, and strong technical support is provided for realizing efficient and sustainable electrochemical conversion process.

[0029] 3、The modified catalyst prepared by the application exhibits significant simplification efficiency in the preparation process of catalyst ink, and the dispersibility and stability of the catalyst in the ink are significantly enhanced, thereby reducing the complexity of the formula. This improvement helps to simplify the production steps and improve the consistency and quality of the product, which has a positive significance for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Flow chart for carbon nanotube purification (a), carbon nanotube oxidation (b), carbon nanotube supported molecular catalyst (c), and hydrophobic modification of carbon nanotubes (d) in the preparation method described in Example 1;

[0031] Figure 2 SEM image of oxidized carbon nanotubes;

[0032] Figure 3 SEM image of carbon nanotubes loaded with molecular catalysts and subjected to hydrophobic modification;

[0033] Figure 4 Catalytic performance of carbon nanotube molecular catalysts without hydrophobic modification and with hydrophobic modification under different current densities;

[0034] Figure 5 Stability of carbon nanotube molecular catalysts without hydrophobic modification and with hydrophobic modification at 100 mA / cm 2

[0035] Figure 6 (a) Contact angle results and (b) catalytic performance of carbon nanotube molecular catalysts modified with different silanes;

[0036] Figure 7 Catalytic performance of carbon nanotube molecular catalysts with different degrees of oxidation and subjected to hydrophobic modification under different current densities. DETAILED DESCRIPTION

[0037] The technical solutions of the application will be further described below through specific embodiments. It should be understood that the implementation of the application is not limited to the following examples, and any form of modification and / or change of the application will fall within the scope of the application.

[0038] ​In the present application, all parts, percentages and proportions referred to in the specification and claims are by weight, unless otherwise specified. All such other equipment and materials as are needed, or desired, for practicing the application and which are not otherwise described in the specification can be employed.

[0039] The reagents used in the following examples, unless otherwise specified, can be purchased from a conventional biochemical reagent store.

[0040] YLS-30T carbon paper, i.e. fuel cell gas diffusion layer carbon paper substrate, commercially available.

[0041] Nafion ionomer, aqueous solution of Nafion TM Polymer dispersant, i.e. Nafion 117 solution (McMaster Carr N831951 Nafion 117 perfluorinated resin solution, ~5% in a mixture of lower aliphatic alcohols and water), Cas No: 31175-20-9, commercially available.

[0042] Example 1

[0043] A method for preparing a carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst, the specific steps are as follows:

[0044] 1. Purification of carbon nanotubes

[0045] A sample of 1 g of commercially available carbon nanotubes was placed in a muffle furnace and heated at 500°C for 60 min, then stopped heating, and the sample was taken out after cooling to room temperature. The above-mentioned carbon nanotubes were placed in a 250 ml flask and 70 ml of 6 mol / L hydrochloric acid solution was added, and it was ensured that the carbon nanotubes were in full contact with the hydrochloric acid solution. After heating at 140°C for 2 h using an oil bath, it was cooled to room temperature, washed three times by centrifugation using ultrapure water, and then placed in a freeze dryer to obtain a purified carbon nanotube sample.

[0046] 2. Oxidation of carbon nanotubes

[0047] Put 1 g of purified carbon nanotubes into a 250 ml round bottom flask, add 23 ml of concentrated sulfuric acid (mass concentration about 98%), and stir overnight at room temperature; transfer the above solution to a water bath for heating, when the temperature rises to 40°C, add 350 mg of sodium nitrate; slowly add 1 g of potassium permanganate while keeping the reaction temperature below 45°C; continue to stir the solution at 40°C for 30 min; then add 3 ml of water to the flask, and after 5 min, add another 3 ml of water. After another 5 min, add 40 ml of water; 15 min later, remove the flask from the water bath, add 140 ml of water and 10 ml of 30% mass concentration hydrogen peroxide to end the reaction; wash the oxidized carbon nanotubes by repeatedly using 5% mass concentration HCl solution and water, and then freeze-dry to obtain the oxidized carbon nanotubes.

[0048] 3. Loading of molecular catalyst

[0049] Ultrasonically disperse 30 mg of the oxidized carbon nanotubes in 20 ml of DMF using an ultrasonic dispersion device with a power of 1800 W for 1 h to obtain a CNT suspension.

[0050] Ultrasonically disperse 3 mg of CoPc in another 10 ml of DMF, and then add to the above CNT suspension, further ultrasonically disperse for 1 h and stir at room temperature for 24 h. The obtained solid is separated by centrifugation and washed with DMF, ethanol and water by centrifugation, and freeze-dried to obtain the CO2 reduction catalyst CoPc MDE-O.

[0051] 4. Hydrophobic modification of carbon nanotubes

[0052] Take 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane as an example to hydrophobize the carbon nanotubes.

[0053] Prepare a mixed solution of ethanol and water, in which the mass ratio of ethanol to water is 1.5:1; add the 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane solution to the above ethanol solution, the concentration of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane is 3 wt%, and stir at room temperature for 2 h to promote the hydrolysis of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane.

[0054] To the hydrolyzed 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane solution, CoPc MDE-O was added, with the mass ratio of CoPc MDE-O to 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane being 20:1, and stirring was carried out under 48°C water bath heating for 2.5h; the CoPc MDE-O and 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane suspension was heated to 75°C and kept for 15min to graft 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane to the surface of CoPc MDE-O, and the grafted CoPc MDE-O was heated to boiling and kept for 30min to promote further grafting of silanol groups. The treated CoPc MDE-O was centrifugally washed in ethanol solution for three times to remove unreacted 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane reagent, and then freeze-dried to obtain the final product CoPc MDE-1.0Si-1.

[0055] The SEM image of the oxidized carbon nanotubes obtained in Step 2 is shown in Figure 2 , and the SEM image of the carbon nanotubes loaded with molecular catalysts and hydrophobically modified is shown in Figure 3 . As shown in Figure 2 , the diameter of the oxidized carbon nanotubes prepared in this embodiment did not change significantly, and no obvious structural damage or deformation was observed under an electron microscope, and the original structural characteristics and morphology could be maintained, proving that the carbon nanotubes maintained their structural stability during the oxidation process. As shown in Figure 3 , the hydrophobically modified carbon nanotubes prepared in this embodiment still maintained the original morphology, arranged uniformly on the carbon paper surface, and the overall structure had no obvious defects, indicating that the silane grafting process would not affect the structural characteristics of the carbon nanotubes.

[0056] Test Example 1

[0057] Preparation of CoPc MDE catalyst (comparative example): A sample of 1 g of commercially available carbon nanotubes was placed in a muffle furnace, heated at 500 °C for 60 min, and then the heating was stopped. After cooling to room temperature, the sample was removed. The carbon nanotubes were placed in a 250 ml flask and 70 ml of 6 mol / L hydrochloric acid solution was added, and the carbon nanotubes were ensured to be in full contact with the hydrochloric acid solution. After heating at 140 °C for 2 h using an oil bath and cooling to room temperature, the sample was centrifuged three times using ultrapure water and then placed in a freeze dryer to obtain a purified carbon nanotube sample. The obtained 30 mg of carbon nanotubes (without oxidation treatment) were ultrasonically dispersed in 20 ml of DMF using an ultrasonic dispersion device with a power of 1800 W for 1 h to obtain a CNT suspension. 3 mg of CoPc was ultrasonically dispersed in another 10 ml of DMF, and then added to the above-mentioned CNT suspension, and further ultrasonically dispersed for 1 h and stirred at room temperature for 24 h. The obtained solid was separated by centrifugation and washed with DMF, ethanol and water, and freeze-dried to obtain the CO2 reduction catalyst CoPc MDE.

[0058] The CoPc MDE-1.0Si-1 and CoPc MDE catalyst inks in Example 1 were prepared and further prepared into working electrodes with a working area of 1 cm 2 The catalytic performance of the CoPc MDE-1.0Si-1 and CoPc MDE catalyst electrodes was tested at different current densities in a 1 M KHCO3 solution. The specific steps are as follows:

[0059] S1. Preparation of catalyst ink

[0060] The preparation method of the CoPc MDE catalyst ink is as follows: 8 mg of CoPc MDE catalyst powder is dispersed in 3.6 ml of isopropyl alcohol, and then 0.8 mg of Nafion ionomer (10 wt% of the catalyst, added in the form of a polymer dispersant) is added. TM

[0061] The preparation method of the CoPc MDE-1.0Si-1 catalyst ink is as follows: 8 mg of CoPc MDE-1.0Si-1 catalyst powder is dispersed in 3.6 ml of isopropyl alcohol, and then 0.8 mg of Nafion ionomer (10 wt% of the catalyst, added in the form of a polymer dispersant) is added. TM

[0062] S2. Preparation of working electrode

[0063] After the catalyst ink prepared in S1 is dispersed under high-power ultrasonic for 1 h, the catalyst ink is loaded on YLS-30T carbon paper until the loading amount of the catalyst reaches 1 mg / cm 2 ​​The loading method can be a drop coating method or a spray coating method. This embodiment adopts the drop coating method; a heating table at 40°C is used to heat the YLS-30T carbon paper to promote the volatilization of isopropyl alcohol during the electrode preparation process.

[0064] The catalytic performance test results of carbon nanotube molecular catalysts without hydrophobic modification and hydrophobic modification at different current densities are as follows: Figure 4 As shown in Figure 2, CoPc MDE-1.0Si-1 exhibits excellent catalytic performance at all current densities, with the CO Faradaic efficiency always maintained above 98%. In contrast, CoPc MDE has difficulty in effectively maintaining the hydrophobicity of the electrode, and the CO Faradaic efficiency is not as good as that of CoPc MDE at 150 and 200 mA / cm 2 A CO Faradaic efficiency of over 95% can be achieved at current densities of 250 mA / cm 2 Gradually increase to 350mA / cm 2 , its Faradaic efficiency gradually dropped to 88%.

[0065] Test Example 2

[0066] The two working electrodes prepared in Test Example 1 were charged in 1M KHCO3 solution at a current density of 100 mA / cm 2 Conduct stability testing.

[0067] The carbon nanotube molecular catalyst without hydrophobic modification and hydrophobic modification is 100mA / cm 2 The stability test results are as follows Figure 5 As shown. Figure 5 As can be seen in the graph, the CoPc MDE electrode exhibits a rapid increase in Faradaic efficiency, maintaining a CO Faradaic efficiency above 90% for only approximately 160 hours. In contrast, the CoPc MDE-1.0Si-1 electrode maintains a relatively stable Faradaic efficiency throughout the test, exceeding 700 hours. It maintains a Faradaic efficiency above 97% for less than 600 hours and maintains a 95% Faradaic efficiency throughout the entire test. This result demonstrates that CoPc MDE-1.0Si-1 exhibits significantly superior stability in the CO2RR compared to CoPc MDE. As previously mentioned, hydrophobic modification of carbon nanotubes significantly enhances the hydrophobicity of the resulting catalyst, maintaining high stability during the reaction and effectively preventing the electrolyte from entering the electrode's micro- and nanoporous structures, thereby maintaining a high Faradaic efficiency over extended reaction times.

[0068] Maintaining good stability of catalytic electrode performance during long-term testing is crucial for CO2 reduction reactions in practical applications and has positive significance for large-scale industrial production.

[0069] Test Example 3

[0070] The effects of different CF chains in silane on the hydrophobicity of silane-modified carbon nanotube molecular catalysts were tested. Catalysts were prepared using 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, (3, 3, 3-trifluoropropyl)trimethoxysilane, and hexadecyltrimethoxysilane. The specific preparation methods were the same as those in Example 1. The modified catalysts were named CoPc MDE-1.0Si-1, CoPc MDE-1.0Si-2, and CoPc MDE-1.0Si-3, respectively.

[0071] The contact angle test of different silane-modified carbon nanotube molecular catalysts was conducted using an optical contact angle meter. 3.5 μl of ultrapure water was dropped onto the catalytic electrode surface, and the software of the contact angle meter was used to analyze the contour curve of the droplet shape and calculate the contact angle between the droplet and the electrode surface. The test results are shown in Figure 2. Figure 6 As shown, the contact angles of the three electrodes are CoPc MDE-1.0-Si-1 > CoPc MDE-1.0Si-2 > CoPc MDE-1.0Si-3. Due to differences in the length and content of the carbon-fluorine chains contained in different silanes, electrodes prepared with modified carbon nanotube molecular catalysts exhibit different hydrophobic properties. 1H,1H,2H,2H-perfluorodecyltriethoxysilane, due to its longer CF chains, provides a more optimal hydrophobic environment for the catalytic electrode compared to (3,3,3-trifluoropropyl)trimethoxysilane. In contrast, hexadecyltrimethoxysilane, lacking CF chains, exhibits lower hydrophobicity. This performance difference is particularly pronounced under high current density conditions. 1H,1H,2H,2H-perfluorodecyltriethoxysilane and (3,3,3-trifluoropropyl)trimethoxysilane, which contain CF chains, exhibited excellent catalytic performance at various current densities. However, hexadecyltrimethoxysilane, which only contains CH chains, was unable to maintain a sufficiently hydrophobic environment at high current densities, resulting in decreased catalytic performance. Therefore, by fine-tuning the chemical structure of the silane molecules, the hydrophobicity of the electrode can be systematically controlled, thereby optimizing its application in electrocatalytic reactions.

[0072] Test Example 4

[0073] To test the influence of silane hydrophobic modification on carbon nanotubes with different oxidation degrees on the reaction performance, take 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane as an example, the preparation of the catalyst is carried out according to the method of reference example 1, but the addition amount of sodium nitrate and potassium permanganate is adjusted, in turn: 280 mg of sodium nitrate, 0.8 g of potassium permanganate; 350 mg of sodium nitrate, 1 g of potassium permanganate; 420 mg of sodium nitrate, 1.2 g of potassium permanganate; 490 mg of sodium nitrate, 1.4 g of potassium permanganate, and the prepared catalysts are named as CoPc MDE-0.8Si-1, CoPc MDE-1.0Si-1, CoPc MDE-1.2Si-1, CoPc MDE-1.4Si-1, respectively; at the same time, the CoPc MDE catalyst not subjected to oxidation modification and silane grafting is prepared as a comparison, and the electrode preparation method is referred to test example 1. The enhanced oxidation degree can introduce more hydroxyl groups on the surface of the carbon nanotubes, thereby grafting more silane groups and improving the hydrophobicity of the silane modified carbon nanotubes. Excessive oxidation can damage the graphite structure of the carbon nanotubes, reduce the conductivity of the carbon nanotubes and the loading amount of the molecular catalyst, thereby affecting the catalytic performance.

[0074] The catalytic performance of the carbon nanotube molecular catalysts subjected to hydrophobic modification after different oxidation degrees was tested at a current density of 550 mA / cm 2 The results are shown in Table 1. Figure 7 The different oxidation degrees of the carbon nanotubes cause differences in the performance of the catalytic electrodes, and the performance of CoPc MDE-1.0Si-1 is the best, while the performance of CoPc MDE-1.4Si-1 is relatively poor, which may be due to the fact that excessive oxidation reduces the conductivity of the carbon nanotubes and reduces the loading amount of the molecular catalyst, thereby reducing the active sites and the catalytic efficiency.

[0075] Each of the embodiments in the specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant parts are described in the method part.

[0076] The carbon fluoride chain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst, the preparation method and the application thereof are described in detail. The principles and implementation manners of the present application are described by using specific examples. The above description of the embodiments is only used to help understand the method and core idea of the present application. It should be pointed out that those skilled in the art can make some improvements and modifications to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method for preparing a carbon-based hydrophobic electrocatalytic CO2 reduction catalyst modified by a carbon-fluorine chain, characterized in that The method comprises the following steps: S1. Heating the carbon nanotubes at 400-500°C for 0.5-1.5 hours, cooling to room temperature, acid-washing, purifying, washing, and freeze-drying to remove impurities contained in the carbon nanotubes; S2. The carbon nanotubes obtained by the pretreatment in S1 are heated in a mixed solution of 96-98% concentrated sulfuric acid, sodium nitrate, and potassium permanganate to perform oxidation treatment on the carbon nanotubes to introduce hydroxyl groups, followed by washing and freeze-drying. The ratio of carbon nanotubes: 96-98% concentrated sulfuric acid: sodium nitrate: potassium permanganate is 1 g: 20 ml-23 ml: 280 mg-420 mg: 0.8 g-1.2 g. The oxidation treatment temperature is not higher than 45° C.; S3, ultrasonically treating the oxidized carbon nanotubes obtained by the treatment in S2 in a DMF solvent environment to load the molecular catalyst, washing, and freeze-drying; The molecular catalyst is cobalt phthalocyanine (CoPc) or nickel phthalocyanine; S4, hydrophobically modifying the oxidized carbon nanotubes loaded with the molecular catalyst in S3 with silane in a silane aqueous solution, heating to 45°C-120°C for 2h-4h, centrifuging and washing to remove unreacted reagents, and freeze-drying to obtain a carbon-fluorine chain-modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst; Preparation of silane aqueous solution: silane content is 1wt%~10wt%, the solvent is a mixture of ethanol and water with a mass ratio of 1~2:1, and the silane and solvent are mixed and hydrolyzed for 1~6 hours; The mass ratio of the oxidized carbon nanotubes to the silane is 10:1 to 60:1; the silane is selected from one or more of 1H,1H,2H,2H-perfluorodecyltriethoxysilane, 1H,1H,2H,2H-perfluorododecyltrichlorosilane, (3,3,3-trifluoropropyl)trimethoxysilane, 1-(trimethylsilyl)heptafluoropropane, and 3,3,3-trifluoropropylmethyldimethoxysilane.

2. The preparation method according to claim 1, wherein: S1, the acid washing step is to heat the carbon nanotubes in a 4-8 mol / L hydrochloric acid solution at 130-150° C. for 2 h to 3 h.

3. The preparation method according to claim 1, wherein: The reaction temperature for oxidizing the carbon nanotubes to introduce hydroxyl groups in S2 is 40-45°C.

4. The preparation method according to claim 1, wherein: In S4, the mixture is heated at 40-50°C for 2-3 hours, maintained at 70-80°C for 10-20 minutes, and heated to boiling and maintained for 20-40 minutes to promote sufficient grafting of silanol groups.

5. The preparation method according to claim 1, wherein: The process of introducing hydroxyl groups by oxidation treatment in S2 is as follows: the carbon nanotubes obtained by purification pretreatment are stirred in 96-98% concentrated sulfuric acid at room temperature overnight; sodium nitrate is added when the above solution is heated to 40-45°C; potassium permanganate is slowly added while maintaining the reaction temperature below 45°C; Then continue stirring at 40°C~44°C, add appropriate amount of water intermittently, stop heating after the reaction is sufficient, and add appropriate amount of water and hydrogen peroxide to the system to terminate the reaction.

6. The preparation method according to claim 1, wherein: In S2, the oxidized carbon nanotubes are repeatedly washed with a 5% by mass HCl solution and water.

7. A carbon-fluorochain-modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst obtained by the preparation method as claimed in claim 1.

8. Use of the carbon-fluorochain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst according to claim 7 in the preparation of catalyst ink.

9. Use of the carbon-fluorochain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst according to claim 7 in the preparation of a working electrode.

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