Preparation method and application of sandwich-structured gas diffusion electrode

Abstract

The invention relates to a preparation method and application of a sandwich-structured gas diffusion electrode, and belongs to the fields of electrochemical catalysis, carbon dioxide utilization and renewable energy sources. According to the preparation method, a catalyst layer, a cation layer and a protective layer are prepared on a gas diffusion substrate in a layered manner; the catalytic layer, the cation layer and the protective layer respectively play roles in catalyzing CO2 reduction, adjusting the microenvironment, preventing cation leakage and the like. When applied, the sandwich-structured gas diffusion electrode GDE prepared by the method can be assembled on electrochemical carbon dioxide reduction modules such as a flow battery and a membrane electrode assembly (MEA) to carry out electrochemical reduction reaction of CO2, has high activity and high stability, and can avoid adding inorganic alkali metal cations into catholyte to inhibit hydrogen evolution side reaction. Based on the invention, GDE can be prepared through a microenvironment engineering means, and the performance of the electrochemical reduction reaction of carbon dioxide is improved.

Description

Technical Field

[0001] The present invention belongs to the fields of electrochemical catalysis, carbon dioxide utilization and renewable energy, and specifically relates to a method for preparing a sandwich-structured gas diffusion electrode and the prepared sandwich-structured gas diffusion electrode in electrochemical CO 2 Application in reduction reactions. Background Art

[0002] In response to the global energy crisis and climate change, converting carbon dioxide into chemicals and fuels has become one of the important ways to achieve sustainable economic and social development. Among various technical methods, electrochemical reduction of carbon dioxide (CO 2 RR) can be carried out under mild conditions and is expected to be applied to the resource utilization of carbon dioxide and the development of renewable energy, which has attracted attention from multiple disciplines.

[0003] The gas diffusion electrode (GDE) maintains a high CO concentration in the catalyst surface microenvironment by effectively forming a three-phase reaction interface. 2 concentration and improve mass transfer, so that the current density is several orders of magnitude higher than that of the conventional flat-plate electrodes immersed in the electrode solution, which can greatly increase the electrochemical reaction rate. 2 Feeding will cause changes in the local environment, resulting in a decrease in the activity and stability of GDE prepared based on existing technologies. 2 RR usually adds high concentrations of inorganic alkali metal cations to the cathode liquid to inhibit the hydrogen evolution side reaction. However, regardless of alkaline, neutral, or acidic conditions, the catalyst surface will become partially alkaline due to the high-speed reaction of digesting protons. When the solubility exceeds a certain level, CO 2 It forms a precipitate with the alkali metal. The precipitation will block the gaseous CO 2 The mass transfer pores reduce the hydrophobicity of GDE, bringing the risk of flooding, thus causing CO 2 In addition, due to the use of a cathode liquid containing a high concentration of inorganic alkali metal cations, liquid products such as formic acid and acetic acid will be mixed with alkali metals, requiring additional high-energy downstream processes (such as distillation) for product separation, reducing CO 2 Therefore, it is urgent to innovate the preparation method of GDE, improve the activity and stability through microenvironmental engineering, and avoid adding inorganic alkali metal cations to the cathode liquid to inhibit the hydrogen evolution side reaction. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a sandwich-shaped gas diffusion electrode and its application. The method comprises three layers of a catalyst layer, a cationic layer and a protective layer on a gas diffusion substrate. The catalyst layer, the cationic layer and the protective layer play the role of catalyzing CO 2RR, regulating the microenvironment, preventing cation leakage, etc. The sandwich cathode prepared by this method has high activity and high stability when applied to the electrochemical reduction reaction of carbon dioxide, and avoids adding inorganic alkali metal cations to the cathode liquid to inhibit the hydrogen evolution side reaction. Based on the present invention, GDE can be prepared by microenvironment engineering means to improve the performance of carbon dioxide electrochemical reduction.

[0005] To achieve the above object, the technical solution of the present invention is: a method for preparing a sandwich-shaped gas diffusion electrode, which is divided into three layers on a gas diffusion substrate and prepared according to the following steps: Step 1: Apply a catalytic layer to the gas diffusion substrate Taking a predetermined ratio of catalyst, ionomer powder, and organic alcohol, and mixing them evenly to obtain a conductive ink; applying the conductive ink evenly to a gas diffusion substrate by spraying or dripping, and applying a catalytic layer on the gas diffusion substrate; Step 2: Apply a cationic layer on the catalyst layer Taking a predetermined proportion of alkali metal hydroxide or organic cation, organic alcohol, and ionomer powder, mixing them evenly, and then applying them evenly on the catalyst layer prepared in step 1 by spraying or dripping, and applying a cationic layer on the catalyst layer; Step 3: Apply a protective layer on the cationic layer Take a predetermined ratio of ionomer powder and organic alcohol, mix them evenly, and then evenly apply them to the cationic layer prepared in step 2 by spraying or dripping, and then apply a protective layer on the cationic layer.

[0006] In one embodiment of the present invention, the catalyst in the catalytic layer has the ability to reduce carbon dioxide to obtain one-carbon products including formic acid and CO, or obtain two-carbon and above products including ethylene.

[0007] In one embodiment of the present invention, carbon materials including carbon black, graphene, and carbon nanotubes are added to the conductive ink formed when preparing the catalyst layer to improve the conductivity.

[0008] In one embodiment of the present invention, the formula of the conductive ink is: 0.02-0.5 g of catalyst + 0.005-0.02 g of carbon material + 200-1000 μL of organic alcohol + 50-200 μL of ionomer powder.

[0009] In one embodiment of the present invention, the gas diffusion substrate is a carbon paper type or a polytetrafluoroethylene (PTFE) type.

[0010] In one embodiment of the present invention, the organic alcohol is isopropanol or ethanol.

[0011] In one embodiment of the present invention, the ionomer powder has ion exchange capability, and commercial ionomers including PiperION, Sustainion, QAPPT, Aquivion, Nafion, and Femion are used.

[0012] In one embodiment of the present invention, the alkali metal hydroxide includes KOH and CsOH to provide alkali metal cations with a larger ionic radius.

[0013] In one embodiment of the present invention, the organic cations are cations including imidazoles, pyridines, and quaternary ammonium salts.

[0014] The present invention also provides an application of a sandwich-structured gas diffusion electrode prepared based on the above-mentioned method for preparing a sandwich-structured gas diffusion electrode, wherein the sandwich-structured gas diffusion electrode is assembled in an electrochemical carbon dioxide reduction module including a flow cell and a membrane electrode assembly (MEA) to perform CO 2 The electrochemical reduction reaction has high activity and high stability, and can avoid adding inorganic alkali metal cations to the cathode liquid to inhibit the hydrogen evolution side reaction.

[0015] Compared with the prior art, the present invention has the following beneficial effects: the present invention can construct a sandwich-shaped GDE by means of microenvironment engineering; it does not need to rely on the industrial development of high-performance cathode catalysts; commercial materials are used throughout the process, which is easy to standardize production; it avoids adding inorganic alkali metal cations to the cathode liquid to inhibit the hydrogen evolution side reaction; it can prevent CO 2 Formation of precipitation with alkali metals, resulting in blockage of gaseous CO 2 Mass transfer channels, CO 2 When the sandwich-structured GDE is applied, the reduction of CO 2 When producing liquid products (such as formic acid and acetic acid), the problem of mixing of products with alkali metals does not exist, because the addition of inorganic alkali metal cations to the cathode liquid to inhibit the hydrogen evolution side reaction can be avoided, and the use of additional high-energy consumption downstream processes (such as distillation) for product separation is avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of a GDE structure of a sandwich configuration in a specific embodiment of the present invention.

[0017] Figure 2 Schematic diagram of comparative study of formic acid product generation performance of three GDEs in a specific embodiment of the present invention, including a sandwich-configured GDE, a two-layer structure of a catalytic layer and a cation layer, and a two-layer structure of a cation layer and a protective layer. Figure 3In one embodiment of the present invention, a sandwich-configured GDE is used to perform CO 2 Schematic diagram of the change in the concentration of formic acid produced by the reduction reaction.

[0018] Figure 4 In one embodiment of the present invention, a sandwich-configured GDE is used to perform CO 2 Schematic diagram of the voltage change during the reduction reaction.

[0019] Explanation of reference numerals: 1 - catalytic layer; 2 - cation layer; 3 - protective layer; 4 - gas diffusion substrate. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0021] The present invention provides a method for preparing a sandwich-type gas diffusion electrode, which is divided into three layers on a gas diffusion substrate and prepared according to the following steps: Step 1: Apply a catalytic layer to the gas diffusion substrate Taking a predetermined ratio of catalyst, ionomer powder, and organic alcohol, and mixing them evenly to obtain a conductive ink; applying the conductive ink evenly to a gas diffusion substrate by spraying or dripping, and applying a catalytic layer on the gas diffusion substrate; Step 2: Apply a cationic layer on the catalyst layer Taking a predetermined proportion of alkali metal hydroxide or organic cation and organic alcohol, mixing them evenly, and then applying them evenly on the catalyst layer prepared in step 1 by spraying or dripping, and applying a cationic layer on the catalyst layer; Step 3: Apply a protective layer on the cationic layer Take a predetermined ratio of ionomer powder and organic alcohol, mix them evenly, and then evenly apply them to the cationic layer prepared in step 2 by spraying or dripping, and then apply a protective layer on the cationic layer.

[0022] The present invention also provides an application of a sandwich-structured gas diffusion electrode prepared based on the above-mentioned method for preparing a sandwich-structured gas diffusion electrode, wherein the sandwich-structured gas diffusion electrode is assembled in an electrochemical carbon dioxide reduction module including a flow cell and a membrane electrode assembly (MEA) to perform CO 2 The electrochemical reduction reaction has high activity and high stability, and can avoid adding inorganic alkali metal cations to the cathode liquid to inhibit the hydrogen evolution side reaction.

[0023] The following are specific implementation examples of the present invention.

[0024] Example 1 In this embodiment, combined with Figure 1, a sandwich-shaped GDE structure in a specific embodiment of the present invention is described, which includes: The gas diffusion substrate 4 may be a carbon paper type or a polytetrafluoroethylene (PTFE) type. In the present invention, the preferred gas diffusion substrate is a carbon paper type SIGRACET 39BB.

[0025] Catalytic layer 1, take a certain proportion of catalyst, ionomer powder, and organic alcohol, mix them evenly to obtain conductive ink. The conductive ink is evenly applied to the gas diffusion substrate by spraying, dripping, etc., so as to achieve a catalytic layer on the gas diffusion substrate. In the present invention, a solution prepared by adding: 0.5 g bismuth nanoparticles, 0.015 g carbon black, 500 μL isopropanol, and 100 μL Sustainion (5% mass concentration) ionomer powder is added to a 2.5 ml centrifuge tube. Ultrasonicate for 20 minutes and mix evenly. Use a spray gun to spray the mixed solution onto the gas diffusion substrate under a nitrogen flow.

[0026] Cationic layer 2, a cationic mixed solution is sprayed on the catalyst layer 1 using a spray gun under a nitrogen flow. In the present invention, the cationic mixed solution is composed of the following components: 500 μL 0.2 M KOH, 250 μL ethanol, and 10 μL Sustainion (5% mass concentration) ionomer powder prepared solution.

[0027] Protective layer 3, a protective mixed solution is sprayed on the cationic layer 2 using a spray gun under a nitrogen flow. In the present invention, the protective mixed solution is composed of the following components: 1000 μL ethanol, 50 μL Sustainion (5% mass concentration) ionomer powder prepared solution.

[0028] Example 2 In this embodiment, combined with Figure 2 In a specific embodiment of the present invention, the performance of carbon dioxide reduction reaction using a sandwich-configured GDE is studied to illustrate the superiority of the sandwich configuration. GDE is prepared in three ways, including a sandwich-configured GDE with a 3-layer structure, a 2-layer structure in which a catalyst layer and a cation layer are mixed, and a 2-layer structure in which a cation layer and a protective layer are mixed. In the present invention, the electrochemical carbon dioxide reduction module is a membrane electrode assembly (MEA), and its cathode is a GDE prepared by the above three methods. Constant voltage operation is performed at a cell voltage of 4 V. The results show that the formic acid concentration of the sandwich-configured GDE is higher than that of the other two GDEs, and the formic acid production performance is stable during operation. It can be seen that the sandwich-configured GDE has the best operating stability and formic acid production performance, and the sandwich configuration has superiority.

[0029] Example 3 In this embodiment, combined with Figure 3 and Figure 4 In one embodiment of the present invention, a sandwich-shaped GDE is used to perform CO 2 During the reduction experiment, the changes in the concentration of formic acid and the voltage generated are explained. The electrochemical carbon dioxide reduction module is a membrane electrode assembly (MEA) equipped with a solid electrolyte: the anode is platinum-coated titanium felt, the electrochemical carbon dioxide reduction module is filled with 0.8 g of cation exchange resin as a solid electrolyte, and the cathode is a sandwich-configured GDE. The cathode liquid is pure water, that is, the addition of inorganic alkali metal cations to the cathode liquid to inhibit the hydrogen evolution side reaction is avoided. The electrochemical carbon dioxide reduction module operates at a constant current of 240 mA, and the cathode liquid flows unidirectionally. The electrochemical carbon dioxide reduction module was powered on and it was found that within 125 hours, the change in the concentration of formic acid in the effluent ( Figure 3 )、Voltage changes( Figure 4 ) is stable, and finally a formic acid solution of more than 3 L and a concentration of more than 5 g can be collected. In summary, the sandwich-shaped GDE involved in the present invention can be assembled in an electrochemical carbon dioxide reduction module to perform CO 2 The electrochemical reduction of 2-Hydrogen-containing electrolyte has high activity and stability, and avoids adding inorganic alkali metal cations to the cathode liquid to inhibit the hydrogen evolution side reaction.

[0030] Although the present invention has been described in detail, modifications within the spirit and scope of the present invention will be apparent to those skilled in the art, and the above description is intended only as an example and is not intended to limit the present invention.

[0031] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions do not exceed the scope of the technical solution of the present invention, belong to the protection scope of the present invention.

Claims

1. A method for preparing a sandwich-type gas diffusion electrode, characterized in that: Divide into 3 layers on the gas diffusion substrate and prepare according to the following steps: Step 1: Apply a catalytic layer to the gas diffusion substrate Taking a predetermined ratio of catalyst, ionomer powder, and organic alcohol, and mixing them evenly to obtain a conductive ink; applying the conductive ink evenly to a gas diffusion substrate by spraying or dripping, and applying a catalytic layer on the gas diffusion substrate; Step 2: Apply a cationic layer on the catalyst layer Taking a predetermined proportion of alkali metal hydroxide or organic cation, organic alcohol, and ionomer powder, mixing them evenly, and then applying them evenly on the catalyst layer prepared in step 1 by spraying or dripping, and applying a cationic layer on the catalyst layer; Step 3: Apply a protective layer on the cationic layer Take a predetermined ratio of ionomer powder and organic alcohol, mix them evenly, and then evenly apply them to the cationic layer prepared in step 2 by spraying or dripping, and then apply a protective layer on the cationic layer.

2. The method for preparing a sandwich-structured gas diffusion electrode according to claim 1, characterized in that: The catalyst in the catalytic layer has the ability to reduce carbon dioxide to obtain one-carbon products including formic acid and CO, or obtain two-carbon and above products including ethylene.

3. The method for preparing a sandwich-structured gas diffusion electrode according to claim 1, characterized in that: Carbon materials including carbon black, graphene, and carbon nanotubes are added to the conductive ink formed when preparing the catalyst layer to improve conductivity.

4. The method for preparing a sandwich-type gas diffusion electrode according to claim 3, characterized in that: The formula of the conductive ink is: 0.02~0.5 g of catalyst + 0.005~0.02 g of carbon material + 200~1000 μL of organic alcohol + 50~200 μL of ionomer powder.

5. The method for preparing a sandwich-structured gas diffusion electrode according to claim 1, characterized in that: The gas diffusion substrate is of carbon paper type or polytetrafluoroethylene (PTFE) type.

6. The method for preparing a sandwich-structured gas diffusion electrode according to claim 1, characterized in that: The organic alcohol is isopropanol or ethanol.

7. The method for preparing a sandwich-structured gas diffusion electrode according to claim 1, characterized in that: The ionomer powder has ion exchange capability, and commercial ionomers including PiperION, Sustainion, QAPPT, Aquivion, Nafion, and Femion are used.

8. The method for preparing a sandwich-structured gas diffusion electrode according to claim 1, characterized in that: The alkali metal hydroxide includes KOH and CsOH to provide an alkali metal cation having a larger ionic radius.

9. The method for preparing a sandwich-structured gas diffusion electrode according to claim 1, characterized in that: The organic cations include cations of imidazoles, pyridines, and quaternary ammonium salts.

10. An application of a sandwich-structured gas diffusion electrode prepared by the method for preparing a sandwich-structured gas diffusion electrode according to any one of claims 1 to 9, characterized in that: The electrochemical carbon dioxide reduction module is assembled in a flow battery and a membrane electrode assembly (MEA) to carry out the electrochemical reduction reaction of CO2. It has high activity and high stability and can avoid adding inorganic alkali metal cations to the cathode liquid to inhibit the hydrogen evolution side reaction.

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