Membrane electrode structure for acidic electrocatalytic carbon dioxide reduction and method of preparation

Abstract

The application belongs to the field of electrocatalytic electrode preparation and utilization, and discloses a membrane electrode structure and a preparation method for acid electrocatalytic carbon dioxide reduction based on carbon paper coated with a catalyst. The catalyst is first sprayed on the carbon paper, and then a certain amount of polytetrafluoroethylene particles and a cationic ionomer mixed solution are sprayed on the catalyst layer to form a gas diffusion electrode with a functional layer. Finally, a membrane electrode assembly is assembled and laminated. The cationic ionomer is a polyimidazole cationic polymer or a polyquaternary ammonium salt cationic polymer. The application designs and prepares a membrane electrode for acid electrocatalytic carbon dioxide reduction. The hydrogen evolution reaction is inhibited by forming a functional layer on the catalyst layer by using cationic ionomers and polytetrafluoroethylene particles. The electrode has a high electrocatalytic carbon dioxide reduction Faraday current efficiency under acidic conditions.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic electrode preparation and utilization, and particularly relates to an acidic electrocatalytic carbon dioxide reduction membrane electrode structure and preparation method based on a carbon paper coated catalyst. Background Technology

[0002] Carbon dioxide is one of the major greenhouse gases, and my country emitted approximately 11.9 billion tons of carbon dioxide in 2020. Under the carbon neutrality strategy, carbon dioxide capture has received increasing research attention in order to reduce atmospheric carbon dioxide emissions, showing broad development prospects and huge market value. Electrocatalytic CO2 reduction technology utilizes clean electricity to convert the greenhouse gas CO2 into high-value fuels and chemicals, representing a promising new carbon-negative technology. Among these technologies, the membrane electrode assembly (MEA) has a simple structure. Typically, a gas diffusion electrode is prepared by spraying a catalyst onto carbon paper, and then stacking the gas diffusion electrode, ion exchange membrane, and anode between the anode and cathode. An electrolyte is introduced through the anode, and the CO2 reaction gas is introduced through the cathode. Theoretically, MEAs have the lowest system internal resistance and high CO2 diffusion capacity, making them the most promising for scale-up applications. Currently, MEAs operate under three main conditions: alkaline, neutral, and acidic. MEAs operating under alkaline and neutral conditions typically employ anion exchange membranes. In these cases, the CO2 gas introduced at the cathode inevitably reacts with existing hydroxide ions in the electrolyte or hydroxide ions produced by water decomposition. The resulting bicarbonate or carbonate ions pass through the anion exchange membrane to the anode, causing CO2 loss and difficulty in electrolyte regeneration. MEAs operating under acidic conditions utilize cation exchange membranes, such as Nafion membranes, which effectively avoid the CO2 loss problems associated with alkaline and neutral conditions and have significant development potential. However, under acidic conditions, a large number of hydrogen ions (H+) are present. + Hydrogen is easily transported from the anolyte to the cathode catalyst surface under the influence of electric field force and concentration difference, exacerbating hydrogen evolution at the cathode and reducing the current efficiency of the CO2 reduction reaction, thus hindering the development of this type of acidic MEA electrode electrocatalytic CO2 reduction technology. Therefore, developing new strategies to improve the efficiency of acidic MEA electrocatalytic CO2 reduction is of great significance.

[0003] Based on the above analysis, the main problem with existing acidic MEA electrocatalytic CO2 reduction is: a large amount of H₂... + Under the influence of current and concentration difference, hydrogen passes through the cation exchange membrane, resulting in severe hydrogen evolution at the cathode and reducing the reaction current efficiency of electrocatalytic CO2 reduction. Summary of the Invention

[0004] To address the problems associated with the electrocatalytic CO2 reduction of acidic MEAs, this invention provides a novel structure and preparation method for a new MEA electrode. This method is simple to operate, and the prepared gas diffusion electrode and MEA exhibit high electrocatalytic CO2 reduction current efficiency under acidic conditions.

[0005] This invention is achieved by laminating a gas diffusion electrode with a separation membrane and an anode electrode to form a MEA. The fabrication processes for the gas diffusion electrode and the MEA electrode are as follows: Step 1: Prepare the catalyst dispersion by ultrasonically dispersing the catalyst in a mixed solution of anhydrous ethanol and water. After thorough ultrasonic dispersion, the catalyst is evenly sprayed onto a carbon paper substrate using a spraying method and allowed to air dry naturally at room temperature. Step 2: A certain amount of polytetrafluoroethylene particles and a certain amount of cationic ionomer (5 wt.% ethanol solution) are ultrasonically dispersed in isopropanol. The carbon paper coated with the catalyst is placed on an 80°C heating stage, and a certain amount of the polytetrafluoroethylene and cationic ionomer mixture is uniformly coated onto the catalyst by spraying to complete the preparation of the gas diffusion electrode. Step 3: Stack and press the gas diffusion electrode, cation exchange membrane, and anode electrode to form the MEA electrode.

[0006] Furthermore, the cationic ionomers in step two include imidazolium cationic ionomers and polyquaternary ammonium salt cationic ionomers with long-chain alkyl groups; Furthermore, in the step described, the ratio of ethanol to water is 1:1 to 3:1; Furthermore, in step two, the mass ratio of polytetrafluoroethylene to cationic ionomer ranges from 2:1 to 8:1, and the ratio of polytetrafluoroethylene particles to isopropanol ranges from 2 to 20 milligrams of polytetrafluoroethylene particles to be dispersed per milliliter of isopropanol. Furthermore, in step two, the amounts of the polytetrafluoroethylene and cationic ionomer mixture are: polytetrafluoroethylene loading: catalyst loading 1:2 ~ 3:1.

[0007] The purpose of this invention is to provide a membrane electrode for electrocatalytic carbon dioxide reduction under acidic conditions. The cathode gas diffusion electrode catalyst is coated with a porous functional layer composed of polytetrafluoroethylene and cationic ionomers. This layer slows down the diffusion of hydrogen ions from the anolyte to the cathode, inhibits hydrogen evolution, and thus enables the entire electrode to exhibit high Faraday current efficiency for electrocatalytic carbon dioxide reduction. The electrode is characterized by its simple structure, low manufacturing cost, absence of complex reaction processes, and ease of scale-up.

[0008] The purpose of this invention is to provide a membrane electrode structure for electrocatalysis, comprising: Carbon paper, which includes: Fiber layers are used to provide structural support; Microporous leveling layer, used to provide a smooth surface; The catalyst layer, formed on carbon paper, is used to provide a catalyst for the electrocatalytic reaction; Gas diffusion electrode, comprising: Polytetrafluoroethylene and cationic ionomers are formed on the catalyst layer to protect the catalyst layer and ensure effective gas diffusion; A cation exchange membrane, located on one side of the gas diffusion electrode, is used to allow cations to pass through; The anode, in contact with the cation exchange membrane, is the circuit used to complete the electrocatalytic reaction.

[0009] Furthermore, the catalyst layer is formed by a method of preparing the catalyst into a dispersion and spraying it onto carbon paper to ensure that the catalyst layer is in close contact with the micropore-filling layer of the carbon paper.

[0010] The purpose of this invention is to provide a method for preparing a membrane electrode structure for electrocatalysis, characterized by comprising the following steps: S101: The catalyst is prepared into a dispersion and sprayed onto carbon paper to form a catalyst layer; S102: Polytetrafluoroethylene and cationic ionomer are made into a dispersion, sprayed onto the catalyst layer, and dried to serve as a gas diffusion electrode; S103: A membrane electrode is formed by pressing and assembling a gas diffusion electrode, a cation exchange membrane, and an anode.

[0011] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows: First, the present invention utilizes hydrophobic polytetrafluoroethylene particles and cationic ionomers to add a functional layer to the traditional gas diffusion electrode catalyst layer to obtain a new membrane electrode. This membrane electrode can suppress the hydrogen evolution reaction under acidic conditions, thus exhibiting a high electrocatalytic carbon dioxide reduction Faraday current efficiency.

[0012] Secondly, as supporting evidence of the inventiveness of this invention, it is also reflected in the following important aspects: (1) The expected benefits and commercial value of the technical solution of this invention after transformation are as follows: Based on the preparation of the gas diffusion electrode catalyst layer, a new functional layer is constructed using polytetrafluoroethylene and cationic ionomers to suppress the hydrogen evolution reaction of the membrane electrode under acidic conditions. Therefore, the membrane electrode exhibits a high Faraday current efficiency for electrocatalytic carbon dioxide reduction. The reagents used are inexpensive, and the membrane electrode has advanced and practical potential in electrocatalytic carbon dioxide reduction reactions, thus possessing high commercial value.

[0013] (2) Whether the technical solution of the present invention overcomes technical bias: The present invention can effectively solve the problem that ordinary membrane electrodes are prone to hydrogen evolution under acidic conditions, which is to overcome technical bias.

[0014] Third, the significant technological advancements in this method for preparing membrane electrodes based on carbon paper-coated catalysts for acidic electrocatalytic carbon dioxide reduction include: 1. Improved catalytic efficiency: By using specific catalysts and optimized coating methods, this method improves the catalytic efficiency of electrocatalytic carbon dioxide reduction, thereby improving the overall efficiency of the reaction.

[0015] 2. Optimized material usage: This method optimizes the use of these materials by precisely controlling the ratio of polytetrafluoroethylene particles and cationic ionomers and their distribution on the catalyst layer, thereby improving the performance and durability of the membrane electrode.

[0016] 3. Simplified preparation process: This method can prepare membrane electrodes with excellent performance in one step, which simplifies the preparation process, reduces preparation costs, and improves production efficiency.

[0017] 4. Expanded application areas: Since this method can prepare membrane electrodes for acidic electrocatalytic carbon dioxide reduction, its application in energy, environmental protection and other fields has been expanded.

[0018] The above are all technological advancements, but specific technological advancements still need to be evaluated based on actual applications and test results. Attached Figure Description

[0019] Figure 1 A flow chart of the gas diffusion electrode fabrication process provided in this embodiment of the invention; Figure 2 A structural diagram of the membrane electrode according to an embodiment of the present invention; In the figure: 11, fiber layer of carbon paper; 12, micropore filling layer of carbon paper; 2, catalyst; 31, polytetrafluoroethylene; 32, cationic ionomer; 4, cation exchange membrane; 5, anode.

[0020] Figure 3 Scanning electron microscope images provided in embodiments of the present invention; Figure 4 The reaction performance diagram provided in the embodiments of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] In the technical solution provided by this invention, the connection relationships between the various components are as follows: Preparation of carbon paper: The carbon paper is the basic structure of the electrocatalyst, consisting of a fiber layer 11 and a micropore-filling layer 12. The fiber layer provides structural strength and support for the carbon paper, while the micropore-filling layer provides a smooth surface for the subsequent catalyst layers.

[0023] Catalyst layer formation: A catalyst dispersion is sprayed onto carbon paper to form catalyst layer 2. This layer is kept in place by contact with the micropore-filling layer of the carbon paper and provides the necessary catalyst for the electrocatalytic reaction.

[0024] Formation of the gas diffusion electrode: A gas diffusion electrode is formed by preparing a dispersion of polytetrafluoroethylene 31 and cationic ionomer 32, spraying it onto the catalyst layer, and then drying it. This structure not only protects the catalyst layer but also ensures effective gas diffusion.

[0025] Membrane electrode assembly: The gas diffusion electrode, cation exchange membrane 4, and anode 5 are pressed and assembled into a membrane electrode structure. In this structure, the cation exchange membrane acts as an intermediate layer, allowing cations to pass through but blocking electrons, thereby enabling electrocatalytic reactions to occur between the anode and the gas diffusion electrode.

[0026] Through the above connections, this technical solution provides a compact and fully functional membrane electrode structure for electrocatalysis and its preparation method. The design and material selection of each layer are aimed at ensuring the high efficiency of the electrocatalytic process, as well as the stability and durability of the membrane electrode structure.

[0027] The present invention provides a membrane electrode structure for electrocatalysis and a method for preparing the same, comprising: S101, the catalyst is made into a dispersion and sprayed onto carbon paper to form a catalyst layer; S102: Polytetrafluoroethylene and cationic ionomer are prepared into a dispersion, sprayed onto the catalyst layer, and dried to serve as a gas diffusion electrode. S103 is formed by pressing and assembling a gas diffusion electrode, a cation exchange membrane, and an anode electrode to form a membrane electrode.

[0028] In this invention, the volume ratio of ethanol to water in the dispersion catalyst is 1:1 to 3:1.

[0029] (1) Construction of gas diffusion electrode catalyst layer: 10 mg of silver nanoparticles (particle size about 100 nm) were dispersed in 3 mL of a mixture of ethanol and water in a volume ratio of 1:1, and ultrasonically treated for 1 hour to form a uniform catalyst dispersion; the catalyst dispersion was sprayed onto carbon paper with a leveling layer at a spraying flow rate of 1 mL / min to form a catalyst layer with a catalyst loading of 0.8 mg / cm³.2 Allow to air dry at room temperature; (2) Add 10 mg of polytetrafluoroethylene particles to 2.95 mL of isopropanol solution, add 50 μL of quaternaryammonia poly(N-methyl-piperidine-co-p-terphenyl) (QAPPT) ethanol solution (5% by mass), and sonicate at room temperature for 1 hour to form a polytetrafluoroethylene-cationic ionomer mixed dispersion; place the carbon paper sprayed with catalyst on a heating plate, set the heating temperature to 80 °C, and spray the polytetrafluoroethylene-cationic ionomer mixed dispersion onto the catalyst layer at a spraying flow rate of 1 mL / min and a loading of 0.8 mg / cm³. 2 A polytetrafluoroethylene-cationic ionomer modification layer is formed, which, after drying, serves as a gas diffusion electrode (e.g., Figure 1 (as shown) (3) The above gas diffusion electrode, the perforated polytetrafluoroethylene thin plate, the Nafion membrane, and the titanium mesh-supported iridium oxide / tantalum anode are stacked and pressed into a membrane electrode using MEA anode and cathode plates.

[0030] The embodiments of the present invention have achieved some positive results during the research and development or use process, and have indeed great advantages compared with the prior art. The following content describes them in conjunction with the data, charts and other information of the experimental process.

[0031] The membrane electrode structure prepared by this invention is as follows: Figure 2 As shown, the morphology of the gas diffusion electrode composed of 11, 12, 2, 31, and 32 is as follows. Figure 3 As shown in the scanning electron microscope image, a porous polytetrafluoroethylene-QAPPT capping layer covers the catalyst layer. Under the conditions of acidic potassium sulfate electrolyte (K₂SO₄ concentration 0.1 mol / L, H₂SO₄ concentration 0.1 mmol / L) at the anode and humid carbon dioxide gas at the cathode, the electrocatalytic carbon dioxide reduction performance of the membrane electrode is as follows: Figure 4 As shown, the hydrogen evolution reaction is suppressed, and the membrane electrode operates at 50–300 mA cm⁻¹. -2 It exhibits high carbon monoxide production Faraday current efficiency over a wide current density range, with 100 mA cm⁻¹ being particularly efficient. -2 At the specified current density, the Faraday current efficiency is 96%, and the cell voltage of the electrolytic reactor is only 3.3 V, 300 mA cm⁻¹. -2 The Faraday current efficiency can still reach 80% at the current density, indicating that the membrane electrode has good electrocatalytic carbon dioxide reduction performance under acidic conditions.

[0032] This invention provides a method for preparing a membrane electrode based on a carbon paper-coated catalyst for acidic electrocatalytic carbon dioxide reduction. Its key feature is that the catalyst is first sprayed onto carbon paper, then a mixture of polytetrafluoroethylene particles and cationic ionomer is sprayed onto the catalyst layer to form a gas diffusion electrode with a functional layer, and finally, the membrane electrode assembly is assembled and laminated.

[0033] 1. Prepare a catalyst dispersion in advance by ultrasonically dispersing the catalyst in a mixture of anhydrous ethanol and water. Disperse the catalyst evenly using ultrasonic dispersion, then spray it evenly onto a carbon paper substrate and allow it to air dry at room temperature.

[0034] 2. Prepare a certain amount of polytetrafluoroethylene particles and cationic ionomer (5 wt.% ethanol solution) in advance, and ultrasonically disperse them in isopropanol. Place the carbon paper coated with the catalyst on a heating stage at 80°C, and then use a spraying method to uniformly coat the mixture onto the catalyst to complete the preparation of the gas diffusion electrode.

[0035] This method uses a PTFE particle to cationic ionomer mixture in a ratio of 2:1 to 8:1. Each milliliter of isopropanol contains 2 to 20 milligrams of PTFE particles.

[0036] The cationic ionomer used for spraying onto the catalyst layer is an imidazole cationic ionomer, which is a polyquaternary ammonium salt cationic ionomer with long-chain alkyl groups.

[0037] This preparation method represents a significant technological advancement and is expected to play an important role in the research and application of acidic electrocatalytic carbon dioxide reduction.

[0038] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a membrane electrode based on a carbon paper-coated catalyst for acidic electrocatalytic carbon dioxide reduction, characterized in that, include: (1) Construction of gas diffusion electrode catalyst layer: 10 mg of silver nanoparticles with a particle size of 100 nm were dispersed in 3 mL of a mixture of ethanol and water with a volume ratio of 1:1, and ultrasonically treated for 1 hour to form a uniform catalyst dispersion; the catalyst dispersion was sprayed onto carbon paper with a leveling layer at a spraying flow rate of 1 mL / min to form a catalyst layer with a catalyst loading of 0.8 mg / cm³. 2 Allow to air dry at room temperature; (2) 10 mg of polytetrafluoroethylene (PTFE) particles were added to 2.95 mL of isopropanol solution, followed by 50 μL of 5% QAPPT ethanol solution. The mixture was ultrasonically treated at room temperature for 1 hour to form a mixed dispersion of PTFE and cationic ionomer. Carbon paper coated with catalyst was placed on a heating plate at 80°C. The PTFE-cationic ionomer mixed dispersion was then sprayed onto the catalyst layer at a flow rate of 1 mL / min and a loading of 0.8 mg / cm³. 2 A polytetrafluoroethylene-cationic ionomer modification layer is formed, which is then dried and used as a gas diffusion electrode. (3) The above gas diffusion electrode, the perforated polytetrafluoroethylene thin plate, the Nafion membrane, and the titanium mesh-supported iridium oxide / tantalum anode are stacked and pressed into a membrane electrode using MEA anode and cathode plates.

2. The method for preparing the membrane electrode for acidic electrocatalytic carbon dioxide reduction as described in claim 1, characterized in that, In step two, the mass ratio of polytetrafluoroethylene to cationic ionomer is in the range of 2:1 to 8:1, and the ratio of polytetrafluoroethylene particles to isopropanol is in the range of 2 to 20 mg of polytetrafluoroethylene particles dispersed per milliliter of isopropanol.

3. The method for preparing the membrane electrode for acidic electrocatalytic carbon dioxide reduction as described in claim 1, characterized in that, The amounts of polytetrafluoroethylene particles and cationic ionomer mixture used in step two are: polytetrafluoroethylene loading: catalyst loading 1:2~3:

1.

4. A membrane electrode structure for electrocatalysis prepared by the method according to any one of claims 1 to 3, characterized in that, include: Carbon paper, which includes: Fiber layers are used to provide structural support; Microporous leveling layer, used to provide a smooth surface; The catalyst layer, formed on carbon paper, is used to provide a catalyst for the electrocatalytic reaction; Gas diffusion electrode, comprising: Polytetrafluoroethylene and cationic ionomers are formed on the catalyst layer to protect the catalyst layer and ensure effective gas diffusion. A cation exchange membrane, located on one side of the gas diffusion electrode, is used to allow cations to pass through; The anode, in contact with the cation exchange membrane, is the circuit used to complete the electrocatalytic reaction.

5. The membrane electrode structure according to claim 4, characterized in that, The catalyst layer is formed by a method of preparing the catalyst into a dispersion and spraying it onto carbon paper to ensure close contact between the catalyst layer and the micropore-filling layer of the carbon paper.

6. A method for preparing a membrane electrode structure for electrocatalysis as described in any one of claims 4-5, characterized in that, Includes the following steps: S101: The catalyst is prepared into a dispersion and sprayed onto carbon paper to form a catalyst layer; S102: Polytetrafluoroethylene and cationic ionomer are made into a dispersion, sprayed onto the catalyst layer, and dried to serve as a gas diffusion electrode; S103: Gas diffusion electrode, cation exchange membrane, and anode are pressed and assembled to form a membrane electrode.

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