A composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether and a preparation method thereof

Abstract

The application discloses a kind of composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether and preparation method thereof, belong to electrochemical catalysis technical field, method includes the following steps: with perfluoropolyether, carbon dioxide reduction electrocatalyst is used as raw material, with electronic fluorination liquid as solvent, preparation includes perfluoropolyether and carbon dioxide reduction electrocatalyst dispersion liquid, dispersion liquid is coated to the surface of conductive current collector, dry in oxygen-free atmosphere, obtain the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether;The method is simple, safe, has industrial application potential, can solve the problem that Nafion system is strong hydrophilic, and the composite electrode prepared in CO2RR process has high ethylene faradic selectivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical catalysis, and particularly relates to a composite electrode containing perfluoropolyether for electrocatalytic reduction of carbon dioxide and a preparation method thereof. BACKGROUND

[0002] CO2 is a key medium carrier for renewable energy storage, and has a stable structure in the highest oxidation state at normal temperature and pressure. The activation of the carbon-oxygen double bond needs to overcome a large energy barrier. Electrocatalytic CO2 reduction (CO2RR) is a technology for converting CO2 into high-value carbon-based materials or chemical raw materials using electrical energy. It is a key path for carbon energy recycling. CO2 reduction reaction generally occurs at the cathode, and H2O oxidation reaction occurs at the anode. The efficiency, selectivity, stability, and other properties of the CO2RR process are highly dependent on the design and performance of the catalytic electrode material.

[0003] In order to overcome the problems of low selectivity, low activity, and poor stability in the production of C2H4 by electrocatalytic reduction of CO2, researchers have conducted a large number of studies. For example, the Chinese patent document with publication number CN115595606A discloses a copper-based catalytic electrode, a preparation method thereof, and its application in the electrocatalytic reduction of carbon dioxide to ethylene. The copper-based catalytic electrode of the invention includes a palladium-cuprous oxide catalyst and a conductive current collector. The palladium-cuprous oxide catalyst is loaded on the surface of the conductive current collector. The palladium-cuprous oxide catalyst is formed by loading palladium nanoparticles on the surface of cuprous oxide nanoparticles. The copper-based catalytic electrode exhibits high activity, high selectivity, and stability in the electrocatalytic reduction of carbon dioxide to ethylene. The Chinese patent document with publication number CN112430830A discloses a preparation method and application of an electrode for electrocatalytic reduction of carbon dioxide. The invention first prepares a copper-based macrocyclic compound / carbon electrocatalyst, then weighs the copper-based macrocyclic compound / carbon electrocatalyst, and adds water, alcohol, and Nafion solution in sequence before ultrasonic dispersion to prepare a catalyst slurry. The catalyst slurry is coated on a clean copper substrate. The copper substrate loaded with the copper-based macrocyclic compound / carbon electrocatalyst is further heat-treated to obtain an electrode. The electrode has high CO2 electrocatalytic reduction activity and high selectivity of C2 products at low potential. However, the above-mentioned methods may have problems such as complex steps, difficulty in obtaining raw materials, and complex catalyst systems.

[0004] The regulation of the microenvironment of the catalytic electrode interface directly determines the reaction efficiency of the CO2RR process. The core contradiction of the existing catalytic electrode with low ethylene selectivity may be due to the imbalance of hydrophilicity and hydrophobicity. In the prior art, Nafion (perfluorosulfonic acid polymer) solution is usually used as an electrode binder. The hydrophilic sulfonic acid group (-SO3H) in the perfluorosulfonic acid polymer is easy to form a hydration channel, which enhances the hydrophilicity of the electrode surface, promotes the hydrogen evolution reaction (HER), and blocks the diffusion path of CO2, so that the ethylene selectivity is usually limited to below 40%. Perfluoropolyether, as a liquid fluorinated polymer with no polar group and ultra-low surface energy, can theoretically construct an intrinsic hydrophobic interface. However, it has never been used in an electrocatalytic dispersion system before, and its compatibility with the catalyst and the regulation mechanism of the three-phase reaction interface are unknown. SUMMARY

[0005] In order to solve the core defects of the Nafion system CO2RR catalytic electrode with strong hydrophilicity and low ethylene selectivity in the prior art, the present application provides a composite electrode containing perfluoropolyether for electrocatalytic reduction of carbon dioxide and a preparation method thereof, which has a wide industrial application prospect.

[0006] The specific technical solutions adopted are as follows:

[0007] A preparation method of a composite electrode containing perfluoropolyether for electrocatalytic reduction of carbon dioxide, comprising the following steps: taking perfluoropolyether and an electrocatalyst for carbon dioxide reduction as raw materials, taking an electronic fluorination liquid as a solvent, preparing a dispersion liquid containing perfluoropolyether and an electrocatalyst for carbon dioxide reduction, coating the dispersion liquid on the surface of a conductive current collector, and drying it in an oxygen-free atmosphere to obtain the composite electrode containing perfluoropolyether for electrocatalytic reduction of carbon dioxide.

[0008] The molecular weight of the perfluoropolyether is 1000-10000 g / mol;

[0009] The mass ratio of perfluoropolyether to electrocatalyst for carbon dioxide reduction is 0.1-0.5:1.

[0010] The electrocatalytic reduction of carbon dioxide requires a three-phase interface formed between the reaction gas CO2, the liquid electrolyte and the catalyst body. However, the Nafion binder widely used in the prior art is easy to absorb water and swell due to the presence of sulfonate groups, which destroys the three-phase interface at the catalyst, causes waterlogging, and reduces the catalytic selectivity. Therefore, the present application uses perfluoropolyether to replace the commonly used Nafion, which has the properties of low swelling and strong hydrophobicity, can effectively reduce the swelling phenomenon, stabilize the three-phase interface, and improve the catalytic selectivity.

[0011] Further, the perfluoropolyether is dissolved in the electro-fluorination solution to obtain a perfluoropolyether solution; the electro-catalyst for carbon dioxide reduction is dispersed in the electro-fluorination solution to obtain a uniform catalyst suspension, and the perfluoropolyether solution and the catalyst suspension are mixed to obtain a dispersion liquid containing the perfluoropolyether and the electro-catalyst for carbon dioxide reduction.

[0012] Further preferably, the mass fraction of the perfluoropolyether in the perfluoropolyether solution is 1-10 wt% (further preferably 5-10 wt%), and the mass fraction of the electro-catalyst for carbon dioxide reduction in the catalyst suspension is 0.1-2 wt% (further preferably 0.1-1 wt%).

[0013] Further preferably, ultrasonic treatment is used in the mixing process, and the ultrasonic treatment power is 30-40 KHz, and the duration is 5-30 minutes.

[0014] Preferably, the perfluoropolyether is Z-type perfluoropolyether, the repeating unit is -CF2-CF2-O-, and the molecular weight is 1500-8000 g / mol.

[0015] Further, the electro-catalyst for carbon dioxide reduction is selected from copper-based nanoparticles, silver-based nanoparticles, or tin-based nanoparticles, and the particle size is 1-1000 nm.

[0016] Preferably, the electro-catalyst for carbon dioxide reduction is praseodymium-doped copper oxide nanoparticles, which are prepared by using citric acid, copper nitrate hexahydrate, and praseodymium acetate as raw materials, ethanol as a solvent, constructing a sol-gel reaction system, heating to 150-250℃, drying while stirring to obtain a gel product, and then calcining the gel product at 600-700℃ for 0.5-2 hours.

[0017] Further preferably, 0.5-2 grams of citric acid, 100-300 milligrams of copper nitrate hexahydrate, and 1-90 milligrams of praseodymium acetate are uniformly dissolved in 20 milliliters of ethanol to construct a sol-gel reaction system, and then heated to 150-250℃, dried while stirring to form a gel, to obtain a gel product, and then heated to 600-700℃ for 1 hour to obtain praseodymium-doped copper oxide nanoparticles.

[0018] Specifically, the electro-fluorination solution includes but is not limited to electro-fluorination solution FC-40, electro-fluorination solution FC-43, electro-fluorination solution FC-72, or electro-fluorination solution FC-84, and is preferably electro-fluorination solution FC-40.

[0019] Specifically, the conductive current collector includes but is not limited to carbon paper, carbon felt, foamed metal, metal electrode sheet, or metal mesh.

[0020] Preferably, the dispersion is sprayed or dripped onto the surface of the conductive current collector, and the coating amount of the dispersion is 0.5-2 mg / cm2 in terms of the mass of the electrocatalyst for carbon dioxide reduction in the dispersion. 2 .

[0021] Preferably, the drying is performed in a vacuum environment or a nitrogen atmosphere, the drying temperature is 0-120℃, and the drying time is 0.1-12 hours.

[0022] The application further provides a preparation method of the full-fluoropolyether-containing composite electrode for electrocatalytic reduction of carbon dioxide.

[0023] The application further provides a method for electrocatalytic reduction of carbon dioxide, which applies the full-fluoropolyether-containing composite electrode for electrocatalytic reduction of carbon dioxide.

[0024] Further, the three-electrode system is adopted in the electrocatalytic reduction of carbon dioxide, the full-fluoropolyether-containing composite electrode for electrocatalytic reduction of carbon dioxide is used as the working electrode, the Hg / HgO electrode is used as the reference electrode, and the metal electrode (preferably, the commercial IrO2 / Ti mesh) is used as the counter electrode; the electrolyte used includes the aqueous potassium hydroxide solution or the aqueous sodium hydroxide solution, and the temperature for the electrocatalytic reduction of carbon dioxide is 0-40℃.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] (1) The application provides a full-fluoropolyether-containing composite electrode for electrocatalytic reduction of carbon dioxide and a preparation method thereof, the method is simple and safe, has the potential for industrial application, can solve the problem of strong hydrophilicity of the Nafion system, improve the catalytic selectivity, and significantly reduce the cost of the full-fluoropolyether compared with the Nafion, and the economic benefit is significant.

[0027] (2) The composite electrode prepared by the method has better hydrophobicity, which helps to inhibit the hydrogen evolution reaction and can improve the ethylene Faraday selectivity of the CO2RR process to 53.9%. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The figure is the morphology of the full-fluoropolyether-containing composite electrode for electrocatalytic reduction of carbon dioxide prepared in Example 1.

[0029] Figure 2 The figure is the contact angle of the composite electrode prepared in Example 1 and Comparative Example 1.

[0030] Figure 3 The figure is the data of the electrocatalytic reduction of carbon dioxide of the composite electrode prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0031] In order to make the objects, features and advantages of the present application more clear, the following will be described in detail through specific embodiments. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in many different manners and forms, and the present application is not limited to the embodiments described herein. The technical features of the various embodiments of the present application can be combined appropriately without conflict, and the combinations are also within the scope of the present application.

[0032] The operation methods not specified in the following examples are generally performed according to the conventional conditions or the conditions suggested by the manufacturers. The contents not described in detail in the specification belong to the prior art known to the person skilled in the art. The experimental materials used in the following examples can be purchased from the conventional biochemical reagent companies, unless otherwise specified.

[0033] The perfluoropolyether used in the following examples is a liquid Z-type perfluoropolyether with a molecular weight of 1500-8000 g / mol. The perfluoropolyether and the electronic fluorination liquid FC-40 are commercially available products.

[0034] Example 1

[0035] S1 1 g of perfluoropolyether was dissolved in 19 g of electronic fluorination liquid FC-40 to form a uniform perfluoropolyether solution containing 5 wt% of perfluoropolyether;

[0036] S2 1.0 g of citric acid, 240 mg of copper nitrate hexahydrate and 9 mg of praseodymium acetate were uniformly dissolved in 20 mL of ethanol to construct a sol-gel reaction system, which was then heated to 150°C and dried while stirring until a gel was formed. The gel was then moved into a muffle furnace and heated to 700°C and calcined for 1 hour to obtain praseodymium-doped copper oxide nanoparticle catalyst;

[0037] S3 10 mg of praseodymium-doped copper oxide nanoparticle catalyst was added to 1 mL of electronic fluorination liquid FC-40 and ultrasonically mixed for 20 min at 40 KHz to form a catalyst suspension;

[0038] S4 20 μL of the perfluoropolyether solution prepared in step S1 was added to 1 mL of the catalyst suspension of step S3 and ultrasonically mixed for 20 min at 40 KHz to form a dispersion liquid containing perfluoropolyether and an electrocatalyst for carbon dioxide reduction;

[0039] S5 The dispersion liquid of step S4 was sprayed using an electric air spray gun at a spraying amount of 1 mg / cm 2(Based on the mass of the electrocatalyst for carbon dioxide reduction in the dispersion) it was sprayed onto the surface of carbon paper and dried in a vacuum environment at room temperature for 12 hours to obtain the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether.

[0040] Example 2

[0041] S1 Dissolve 2g of perfluoropolyether in 18g of electronic fluorinated liquid FC-40 to form a homogeneous perfluoropolyether solution containing 10 wt% perfluoropolyether;

[0042] S2 1.0 g of citric acid, 240 mg of copper nitrate hexahydrate and 9 mg of praseodymium acetate were uniformly dissolved in 20 mL of ethanol to construct a sol-gel reaction system. The system was then heated to 150 °C and dried while stirring until a gel was formed. The gel was then transferred to a muffle furnace, heated to 700 °C and calcined for 1 hour to obtain praseodymium-doped copper oxide nanoparticle catalyst.

[0043] S3 10 mg of praseodymium-doped copper oxide nanoparticle catalyst was added to 1 mL of electronic fluorination liquid FC-40 and mixed evenly by ultrasonication at 40 kHz for 20 min to form a catalyst suspension.

[0044] S4 Add 20 μL of the perfluoropolyether solution prepared in step S1 to 1 mL of the catalyst suspension in step S3, and mix evenly by sonication at 40 kHz for 20 min to form a dispersion containing perfluoropolyether and an electrocatalyst for carbon dioxide reduction.

[0045] S5. Using an electric air spray gun, the dispersion from step S4 is sprayed at a concentration of 1 mg / cm³. 2 (Based on the mass of the electrocatalyst for carbon dioxide reduction in the dispersion) it was sprayed onto the surface of carbon paper and dried in a vacuum environment at room temperature for 12 hours to obtain the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether.

[0046] Comparative Example 1

[0047] S1. 1.0 g of citric acid, 240 mg of copper nitrate hexahydrate and 9 mg of praseodymium acetate were uniformly dissolved in 20 mL of ethanol to construct a sol-gel reaction system. The system was then heated to 150 °C and dried while stirring until a gel was formed. The gel was then transferred to a muffle furnace, heated to 700 °C and calcined for 1 hour to obtain praseodymium-doped copper oxide nanoparticle catalyst.

[0048] S2 10 mg of praseodymium-doped copper oxide nanoparticle catalyst was added to 1 mL of ethanol and mixed evenly by sonication at 40 kHz for 20 min to form a catalyst suspension.

[0049] S3 20 μL of commercial Nafion solution (5 wt%) was added into 1 mL of catalyst suspension and mixed uniformly under 40 KHz ultrasonic for 20 min to form a dispersion containing perfluorosulfonic acid polymer and the electrocatalyst for carbon dioxide reduction;

[0050] S4 The dispersion of step S3 was sprayed onto the surface of carbon paper using an electric air spray gun at 1.0 mg / cm 2 (the mass of the electrocatalyst for carbon dioxide reduction in the dispersion) and dried under vacuum at room temperature for 12 hours to obtain a composite electrode.

[0051] Sample analysis

[0052] Electrochemical carbon dioxide reduction reaction: In the electrocatalytic reduction of carbon dioxide, the electrode obtained in the examples and comparative examples was used as the working electrode, the Hg / HgO electrode was used as the reference electrode, and the IrO2 / Ti mesh (commercial product) was used as the counter electrode. The performance of the catalyst was tested in a gas flow electrolysis cell using 1 M KOH aqueous solution as the electrolyte, and the current required for the test was provided by an electrochemical workstation. Constant current electrolysis was carried out at room temperature at different current densities of 400-600 mA / cm 2 , and gas chromatography was used to test the composition and concentration of the gas phase products. It can be seen that under all applied current densities, ethylene is the main product. The faradic efficiency of ethylene generated by the reduction of carbon dioxide by the catalyst of Example 1 at a current density of 600 mA / cm 2 was 53.9%, and the faradic efficiency of hydrogen was only 2.3%.

[0053] Calculation of gas phase faradic efficiency (FE): ;

[0054] In the above formula, n represents the number of electron transfers when CO2 is converted to gas phase products (for example, CO is 2 electrons, CH4 is 8 electrons, C2H4 is 12 electrons, etc.); F represents the faradic constant (96485 C / mol); C i is the volume concentration of the gas phase product detected by gas chromatography (in ppm); I is the total current of the catalyst (in mA); P is the standard atmospheric pressure (1.01 x 10 5 Pa); R is the thermodynamic constant (8.314 J / (mol·K)); T represents the Kelvin temperature, which is room temperature (293.15 K) here; u is the flow rate of CO2 gas (in m 3 / s).

[0055] The experimental results are shown below:

[0056] (1) Table 1 shows the catalytic performance of the composite electrodes prepared in Example 1, Example 2 and Comparative Example 1 in the CO2 electrocatalytic reaction.

[0057]

[0058] (2) Figure 1 The smooth surface of the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether indicates that the catalyst can be uniformly coated on the carbon paper surface.

[0059] (3) Figure 2 The hydrophilicity and hydrophobicity of the composite electrodes prepared in Example 1 and Comparative Example 1 are shown. The contact angle of Example 1 is greater than that of Comparative Example 1, indicating that the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether has better hydrophobicity, which helps to suppress the hydrogen evolution reaction.

[0060] (4) Figure 3 The actual CO2 electroreduction test results of the composite electrodes prepared in Example 1 and Comparative Example 1 are shown. At 400, 500, and 600 mA cm⁻¹, the results were compared with those obtained in the comparative example. -1 At the specified current density, the hydrogen Faraday efficiency of Example 1 was lower than that of Comparative Example 1, while the Faraday efficiency of ethylene was higher than that of Comparative Example 1. The composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether effectively suppressed the hydrogen evolution reaction and improved the Faraday selectivity of ethylene.

[0061] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether, characterized in that, Includes the following steps: Using perfluoropolyether and an electrocatalyst for carbon dioxide reduction as raw materials and electronic fluorinated liquid as solvent, a dispersion containing perfluoropolyether and an electrocatalyst for carbon dioxide reduction is prepared. The dispersion is coated onto the surface of a conductive current collector and dried under an oxygen-free atmosphere to obtain the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether. The molecular weight of perfluoropolyether is 1000-10000 g / mol; The mass ratio of perfluoropolyether to electrocatalyst for carbon dioxide reduction is 0.1-0.5:1; The electrocatalyst for carbon dioxide reduction is praseodymium-doped copper oxide nanoparticles.

2. The method for preparing the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether according to claim 1, characterized in that, First, perfluoropolyether is dissolved in an electronic fluorination liquid to prepare a perfluoropolyether solution; then, an electrocatalyst for carbon dioxide reduction is dispersed in the electronic fluorination liquid to form a uniform catalyst suspension. The perfluoropolyether solution and the catalyst suspension are mixed evenly to obtain a dispersion containing perfluoropolyether and an electrocatalyst for carbon dioxide reduction.

3. The method for preparing the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether according to claim 2, characterized in that, The mass fraction of perfluoropolyether in the perfluoropolyether solution is 1-10 wt%, and the mass fraction of the electrocatalyst for carbon dioxide reduction in the catalyst suspension is 0.1-2 wt%.

4. The method for preparing the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether according to claim 1, characterized in that, The perfluoropolyether is a Z-type perfluoropolyether with a molecular weight range of 1500-8000 g / mol.

5. The method for preparing the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether according to claim 1, characterized in that, The particle size of the electrocatalyst for carbon dioxide reduction is 1-1000 nm.

6. The method for preparing the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether according to claim 1, characterized in that, Praseodymium-doped copper oxide nanoparticles were prepared by the following method: using citric acid, copper nitrate hexahydrate, and praseodymium acetate as raw materials and ethanol as solvent, a sol-gel reaction system was constructed. The system was heated to 150-250℃ to obtain a gel-like product. Subsequently, the gel-like product was calcined at 600-700℃ for 0.5-2 h to obtain praseodymium-doped copper oxide nanoparticles.

7. The method for preparing the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether according to claim 1, characterized in that, Electronic fluorinated fluids include electronic fluorinated fluid FC-40, electronic fluorinated fluid FC-43, electronic fluorinated fluid FC-72, or electronic fluorinated fluid FC-84.

8. The composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether prepared by the method for preparing the composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether according to any one of claims 1-7.

9. A method for electrocatalytic reduction of carbon dioxide, characterized in that, The composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether as described in claim 8 is applied.

10. The method for electrocatalytic reduction of carbon dioxide according to claim 9, characterized in that, A three-electrode system is used for the electrocatalytic reduction of carbon dioxide. The composite electrode for electrocatalytic carbon dioxide reduction containing perfluoropolyether is used as the working electrode, the Hg / HgO electrode is used as the reference electrode, and the IrO2 / Ti mesh is used as the counter electrode. The electrolyte used includes potassium hydroxide aqueous solution or sodium hydroxide aqueous solution, and the temperature for electrocatalytic reduction of carbon dioxide is 0-40℃.

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