Gas diffusion electrode and preparation method and application thereof

Abstract

The invention belongs to the technical field of electrocatalysis, and particularly relates to a gas diffusion electrode and a preparation method and application thereof.The gas diffusion electrode comprises a carbon-based bottom layer, a catalyst layer, a hydrophobic breathable film, a sealing film frame and a power connection frame; the catalyst layer and the hydrophobic breathable film are arranged on the surfaces of the two sides of the carbon-based bottom layer respectively; the sealing film frame, the power connection frame and the catalyst layer are arranged on the surface of the same side of the carbon-based bottom layer, and the sealing film frame and the power connection frame are arranged around the catalyst layer; and the hydrophobic breathable film, the carbon-based bottom layer and the sealing film frame are compounded and molded through a hot pressing method. Compared with the prior art, the defect that in the prior art, a high-temperature heat treatment mode is needed for preparing the gas diffusion electrode is overcome. According to the scheme, the uniform and flat gas diffusion electrode capable of loading the catalyst and ensuring hydrophobicity and breathability is prepared at a relatively low temperature, and different types of catalysts can be loaded to carry out electrochemical reactions in which gas participates.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis technology, specifically relating to a gas diffusion electrode, its preparation method, and its application. Background Technology

[0002] In recent years, the domestic demand and production of hydrogen peroxide have gradually increased, driving continuous innovation in hydrogen peroxide synthesis processes. Compared to the mainstream anthraquinone oxidation method in industry, the electrocatalytic two-electron oxygen reduction synthesis of hydrogen peroxide using water and oxygen as raw materials has the advantages of green and distributed synthesis, avoiding the safety risks of storing and transporting hydrogen peroxide. Applying a gas diffusion electrode loaded with a two-electron oxygen reduction catalyst to the electrosynthesis of hydrogen peroxide is expected to achieve efficient oxygen transport, thereby significantly improving current density and current efficiency, and enabling the concentration of electrosynthesized hydrogen peroxide to reach a range applicable to medical, bleaching, and other fields (0.5-3 wt%).

[0003] As mentioned above, the gas-involved reaction in the electrosynthesis of hydrogen peroxide is very common in electrocatalytic reaction systems. In such reactions, the gaseous reactants react at the interface between the solid electrode and the electrolyte, forming a solid-liquid-gas three-phase interface. To improve the overall efficiency of electrocatalysis, in addition to designing highly efficient and selective catalytic active sites, accelerating the transport of gaseous reactants to the electrode interface is also a problem that must be solved in the reactor. In a single-chamber electrolyzer, the electrode is completely immersed in the electrolyte, and the gas transport rate depends only on the concentration of dissolved gas and the diffusion and convection rates. To improve the gas transport rate, new reactors often have a gas-liquid chamber separation design, with the gas chamber and liquid chamber located on opposite sides of the electrode. The electrochemical reaction takes place in the liquid chamber, while the gas chamber continuously pumps in the gas to participate in the reaction and transports it from the back of the electrode to the catalyst layer to participate in the reaction.

[0004] Based on the reactor design described above, ensuring efficient gas transfer from the gas chamber to the catalyst layer is particularly important. A common practice is to prepare a gas diffusion layer on the electrode, which should have the following characteristics: first, it should have a microporous structure for gas transport; second, it should be water-resistant to prevent the electrolyte from the liquid chamber from entering the gas chamber; and third, it should be chemically stable to prevent corrosion during long-term electrocatalysis and to prevent the "electrode flooding effect" caused by prolonged energization.

[0005] Currently, materials exhibiting both hydrophobicity and good chemical stability are predominantly high-molecular-weight polymers, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), expanded polytetrafluoroethylene (ePTFE), polyethylene, polypropylene, and polydimethylsiloxane (PDMS). These materials are extremely hydrophobic, and their chemical bonds are very stable and not easily broken. Two main techniques exist for fabricating gas diffusion electrodes containing these hydrophobic polymers.

[0006] The first type involves mixing polymers with conductive carbon-based materials, and then rolling the resulting solid onto both sides of a metal mesh to serve as electrodes. For example, patent CN121076057A discloses a method and application for preparing positive electrode rings for lithium manganese button batteries based on a dry electrode process. In this method, electrolytic manganese dioxide powder, a conductive agent, and polytetrafluoroethylene are premixed at low temperature, and a blank is formed by high-speed shearing. Finally, a film is formed by applying high pressure through a heated rolling mill and then die-cutting. The electrode thickness distribution prepared by this method cannot be guaranteed to be uniform, and it requires high-level pretreatment. Inadequate pretreatment can easily lead to the inability to produce a complete and robust positive electrode ring.

[0007] The second type involves immersing sheets of conductive carbon-based material in a relatively dilute polymer slurry for a certain period of time, or coating a polymer emulsion onto the conductive carbon-based material, drying it, and then heat-treating it at a certain temperature to form a gas diffusion layer. For example, patent CN116259766A discloses a method for preparing and applying an integrated carbon paper-microporous layer gas diffusion layer. In this method, carbon paper with grown carbon nanotubes is immersed in an aqueous suspension of polytetrafluoroethylene (PTFE) for 3 minutes, allowing PTFE to adhere to the surface of the carbon paper. The carbon paper is then dried and heat-treated in a muffle furnace for 30 minutes to form the gas diffusion layer. Another example is patent CN105932300A, which discloses a gas diffusion electrode and its preparation method. This electrode consists of a current collector layer, a waterproof and breathable layer, and a catalyst layer. The preparation of the waterproof and breathable layer requires ultrasonically dispersing a hydrophobic material (polymer) in deionized water, filtering it onto a forming mesh, and finally heat-treating it. These two preparation methods are not only cumbersome, but also only applicable to electrodes with very small areas. For electrodes with larger areas (10 cm × 10 cm and above), problems such as uneven distribution of hydrophobic polymers during the drying step causing local water permeability and curling of carbon-based materials during the heat treatment step are likely to occur.

[0008] The heat treatment temperature is also a key parameter determining the performance of gas diffusion electrodes. In existing technologies, heat treatment temperatures are often above 300 °C. At this temperature, the carbon fiber surface is easily oxidized, leading to a decrease in strength, and porous carbon is prone to severe oxidation, causing the pore structure to collapse. For example, patent CN108346805A discloses a gas diffusion electrode and its preparation method, whose electrode consists of a waterproof and breathable layer, a current-collecting conductor, a transition layer, and a catalyst layer. The multi-layered structure of this scheme makes its preparation process complex, and hot pressing is only a pretreatment; the final secondary heat treatment step still requires a high temperature of 350 °C, which easily causes oxidation of the carbon fiber surface and a reduction in structural strength. Therefore, developing a method for preparing a uniform, flat gas diffusion electrode that can support catalysts and ensures hydrophobic and breathable properties at a lower temperature (around 200 °C) remains a challenge that needs to be overcome. Summary of the Invention

[0009] The purpose of this invention is to provide a gas diffusion electrode, its preparation method, and its application to solve at least one of the aforementioned problems, thereby overcoming the shortcomings of existing technologies that require high-temperature (above 300 °C) heat treatment to prepare gas diffusion electrodes. This solution achieves the preparation of a uniform, flat gas diffusion electrode that can support catalysts and maintains hydrophobic permeability at a lower temperature (around 200 °C), and can support different types of catalysts for gas-involved electrochemical reactions.

[0010] The objective of this invention is achieved through the following technical solution: The first aspect of the present invention discloses a gas diffusion electrode, comprising a carbon substrate layer, a catalyst layer, a hydrophobic and gas-permeable membrane, a sealing membrane frame, and an electrical connection frame. The catalyst layer and the hydrophobic and breathable membrane are respectively disposed on both sides of the carbon substrate layer; The sealing film frame and the electrical connection frame are disposed on the same side surface of the carbon substrate layer as the catalyst layer, and the sealing film frame and the electrical connection frame form a closed frame and surround the catalyst layer, and the catalyst layer does not directly contact the electrical connection frame. The outer edge of the hydrophobic and breathable membrane and the closed frame is not less than the outer edge of the carbon substrate layer; The hydrophobic and breathable membrane, the carbon substrate layer, and the sealing membrane frame are compositely formed by hot pressing to ensure that the three are tightly bonded together.

[0011] Preferably, the carbon substrate is carbon fiber cloth, carbon felt or carbon paper, and the thickness of the carbon substrate is 0.1-1 mm.

[0012] Preferably, the hydrophobic and breathable membrane is a composite material, which is composed of polytetrafluoroethylene or expanded polytetrafluoroethylene with a melting temperature higher than the hot-pressing temperature and polyvinylidene fluoride, polyethylene, polypropylene or polydimethylsiloxane with a melting temperature lower than the hot-pressing temperature; the thickness of the hydrophobic and breathable membrane is 50-500 μm and the pore size is 0.05-5 μm.

[0013] Preferably, the sealing membrane frame and the hydrophobic and breathable membrane are made of the same material; The sealing membrane has a U-shaped frame that surrounds the catalyst layer.

[0014] Preferably, the carbon substrate layer is made of a metal with good electrical conductivity, including copper and aluminum; The carbon substrate has an L-shaped structure, with one end connected to an external power source.

[0015] Preferably, the catalyst layer is a catalyst material with two-electron oxygen reduction performance, including carbon-based metal single atoms or metal clusters, metal-organic framework materials, covalent organic framework materials, and metal oxides; The catalyst loading of the catalyst layer is 0.1-5 mg / cm³. 2 .

[0016] A second aspect of this invention discloses a method for preparing a gas diffusion electrode as described in any of the above descriptions, comprising the following steps: S1: The hydrophobic and breathable membrane, the carbon substrate layer and the sealing membrane frame are compositely formed by hot pressing, so that the hydrophobic polymer of the hydrophobic and breathable membrane melts and penetrates into the carbon fiber pores of the carbon substrate layer to form a mechanically interlocked structure. S2: Prepare catalyst slurry and coat it on the side of the carbon substrate layer with the sealing membrane frame, and let it dry naturally to form a catalyst layer; S3: Attach the electrical connection frame to the side of the carbon substrate layer that is composited with the sealing film frame, so that the sealing film frame and the electrical connection frame surround the catalyst layer.

[0017] Preferably, the catalyst slurry is prepared through the following steps: S21: The catalyst is dispersed in ethanol / water or isopropanol / water and ultrasonically prepared to form a catalyst slurry; S22: Add Nafion solution to the catalyst slurry to prepare the catalyst slurry; The water-to-ethanol ratio of ethanol / water or isopropanol / water is 10%-90%, the catalyst content in the catalyst slurry is 2-20 mg / mL, and the ultrasonication time is 10-30 min.

[0018] Preferably, the conditions for the hot pressing method are: pressure 1-10 MPa, hot pressing temperature 150-250 ℃, and hot pressing time 3-10 min.

[0019] A third aspect of the present invention discloses the application of a gas diffusion electrode as described above in a gas-involved electrochemical reaction.

[0020] Preferably, the reactions include two-electron oxygen reduction electrosynthesis of hydrogen peroxide, carbon dioxide reduction, ethylene hydrogenation, nitric oxide oxidation, and other reactions.

[0021] The working principle of this invention is as follows: The hot-pressing method employed in this invention allows the hydrophobic polymer in the hydrophobic breathable membrane and sealing membrane frame to melt and infiltrate into the carbon fiber pores of the carbon substrate, forming a mechanically interlocked structure. Macroscopically, this manifests as a tight bond between the carbon substrate and the gas diffusion layer (hydrophobic breathable membrane). Compared to techniques that involve coating or immersing the carbon substrate in a hydrophobic polymer solution followed by sintering, in this invention, during the hot-pressing process of the hydrophobic composite membrane and carbon substrate, only components in the hydrophobic composite membrane with melting temperatures lower than the hot-pressing temperature melt, preserving the overall framework of the composite membrane. Microscopically, the polymer molecules undergo a certain degree of molecular chain rearrangement, but no drastic phase transition occurs. During the cooling process after hot-pressing, because the overall framework does not completely melt, warping stress is avoided due to asynchronous shrinkage between the hydrophobic layer (hydrophobic breathable membrane, sealing membrane frame) and the carbon substrate, resulting in a flat gas diffusion electrode with a uniformly distributed hydrophobic layer. The advantages of this invention are particularly pronounced for electrodes with larger areas (10 cm × 10 cm and above), as the resulting gas diffusion electrode does not experience severe curling or cracking of the hydrophobic layer. This ensures that: when assembling a flow electrocatalytic device using gas diffusion electrodes, the unevenness of the electrodes will not cause the gas-liquid chamber volume to deviate significantly from the theoretical design value, and the flow field will be uniform without generating a flow field "dead zone"; the hydrophobic layer will not crack, thus ensuring that the electrodes will not become water-permeable and fail during long-term operation of the electrocatalytic device.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, a hydrophobic and breathable (composite) membrane can be tightly fixed on a carbon substrate (conductive carbon-based material) by a single hot pressing method to construct a gas diffusion layer. The resulting gas diffusion electrode is uniform and flat, can be loaded with catalyst, and ensures hydrophobicity and breathability. Moreover, the method is fast and simple, and can be used to prepare gas diffusion electrodes on a large scale and in batches, overcoming the inherent defects of methods such as solid rolling and high-temperature calcination.

[0023] (2) In this invention, by adding a “U”-shaped sealing membrane frame to the side of the catalyst layer, and the “U”-shaped sealing membrane frame is made of the same material as the hydrophobic and breathable membrane, electrolyte leakage can be prevented from the electrode edge after the reactor is assembled.

[0024] (3) In this invention, by bonding an "L"-shaped metal sheet as a grounding frame to the top of the carbon substrate, the potential at the top of the electrode with the bonded "L"-shaped metal sheet is equal when voltage is applied, and the potential changes uniformly on the electrode surface in the direction perpendicular to the metal sheet. This design allows the current to be evenly distributed across the entire electrode, avoiding the accumulation of bubbles in high current density areas, drastic local pH changes, and almost no electrochemical reaction in low current density areas, thus improving the overall electrocatalytic efficiency. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the gas diffusion electrode prepared according to the present invention.

[0026] Figure 2 This is a comparison of the hydrogen peroxide synthesis rate and current efficiency of Examples 1-5 and Comparative Examples 1-3 and 5.

[0027] In the diagram: 1-carbon substrate layer; 2-catalyst layer; 3-hydrophobic and breathable membrane; 4-sealing membrane frame; 5-electrical connection frame. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0029] Unless otherwise specified, the reagents used in the following description are conventional commercial products, the methods used are common knowledge in the field, and any other matters not covered herein can be handled using existing technology.

[0030] A gas diffusion electrode and its preparation method are disclosed, specifically comprising: a conductive carbon-based material as a carbon substrate layer 1, a hydrophobic and gas-permeable membrane 3 on one side, an "L"-shaped metal sheet frame as an electrical connection frame 5, a "U"-shaped sealing membrane frame 4, and a catalyst layer 2 on the other side.

[0031] The conductive carbon-based material is made of carbon fiber cloth, carbon felt or carbon paper, with a thickness of 0.1-1 mm.

[0032] The hydrophobic and breathable composite membrane material for preparing the gas diffusion layer is a composite material composed of one of polytetrafluoroethylene (PTFE) or expanded PTFE and one of polyvinylidene fluoride (PVDF), polyethylene, polypropylene, or polydimethylsiloxane. The membrane thickness is 50-500 μm and the pore size is 0.05-5 μm. PTFE or PVDF has a melting temperature above 300 ℃ and will not melt at the hot-pressing temperature of this scheme, thus preserving its microporous structure for gas diffusion and making it an essential component of the gas diffusion layer. The other component (PVDF, polyethylene, polypropylene, or polydimethylsiloxane) has a melting temperature below 200 ℃. It melts at the hot-pressing temperature and penetrates into the pores of the carbon fibers of the conductive carbon-based material, forming a mechanically interlocking structure, thereby ensuring a tight bond between the carbon substrate layer and the gas diffusion layer.

[0033] The catalyst used in the catalyst layer is a material with two-electron oxygen reduction properties, including carbon-based metal single atoms or metal clusters, metal-organic framework materials, covalent organic framework materials, and metal oxides. It is prepared through the following steps: (1) Weigh a certain mass of catalyst to make the catalyst loading of the gas diffusion electrode 0.1-5 mg / cm³.2 .

[0034] (2) Disperse the catalyst using an ethanol / water or isopropanol / water mixture, wherein the catalyst content in the mixture is 2-20 mg / mL, the water-to-ethanol ratio is 10%-90%, and a homogeneous slurry is prepared after sonication for 10-30 min. (3) Add 5 wt% Nafion solution with a volume fraction of 3%-6% to the slurry prepared in (2).

[0035] (4) The slurry prepared in (3) is coated on the back side of the carbon-based material with the gas diffusion layer assembled. After coating a single layer of slurry, it is allowed to dry naturally. The process is repeated until the slurry is used up.

[0036] To prevent electrolyte leakage from the electrode edges after assembly into the reactor, this scheme adds a "U"-shaped sealing membrane frame to the edge of the catalyst layer on one side of the conductive carbon-based material. The specific implementation method is as follows: select the same material as the aforementioned hydrophobic and breathable membrane, make it into a "U" shape, and place the hydrophobic and breathable membrane, conductive carbon-based material, and "U"-shaped sealing membrane frame in sequence on the hot press sample stage during hot pressing. Apply a certain pressure and maintain it at a certain temperature for a certain time to make the three fully adhere together. Then, hot press and fix them together, and then remove the heat source and take out the sample.

[0037] The hot pressing conditions are: pressure 1-10 MPa, hot pressing temperature 150-250 ℃, and hot pressing time 3-10 min.

[0038] To ensure uniform current density distribution, this scheme uses an "L"-shaped metal sheet frame as a contact frame, bonded to the top of the carbon substrate layer (catalyst layer side). The metal sheet frame is directly connected to an external power source, which reduces contact resistance. Specifically, a thin adhesive tape made of conductive metals such as copper or aluminum is adhered to the top of the carbon-based catalyst side, but does not directly contact the catalyst layer.

[0039] Meanwhile, the "L"-shaped metal sheet frame and the "U"-shaped sealing membrane frame form a closed ring frame surrounding the catalyst layer.

[0040] This solution also provides an application of the aforementioned gas diffusion electrode in the field of electrocatalysis, specifically for the electrosynthesis of hydrogen peroxide via two-electron oxygen reduction. The specific implementation method is as follows: the surface of the electrode's carbon substrate is coated with a catalyst possessing two-electron oxygen reduction properties, including carbon-based metal single atoms or metal clusters, metal-organic framework materials, covalent organic framework materials, metal oxides, etc. After this step, the gas diffusion electrode is assembled into a reactor containing a gas-liquid dual-chamber system. Air is introduced into the gas chamber, and an electrolyte is introduced into the liquid chamber, leading to the electrosynthesis of hydrogen peroxide.

[0041] Furthermore, the application scope of this gas diffusion electrode can be extended to electrochemical reactions involving a variety of gases, including carbon dioxide reduction, ethylene hydrogenation, and nitric oxide oxidation.

[0042] Example 1 Take one piece each of carbon cloth and polytetrafluoroethylene / polypropylene hydrophobic and breathable composite membrane, each with an area of ​​20×20 cm. 2 Next, take another piece of the hydrophobic and breathable composite membrane and cut it into a "U"-shaped sealing membrane frame, with an outer edge length of 20 cm and a frame width of 1 cm. Place the hydrophobic and breathable composite membrane, carbon cloth, and "U"-shaped sealing membrane frame in sequence on the sample stage of the hot press. Apply a pressure of 5 MPa at a hot pressing temperature of 200℃ for 3 minutes to ensure that the three are fully bonded. Then remove the heat source and take out the sample.

[0043] Then, a catalyst layer was coated on the back side of the carbon cloth on which the gas diffusion layer was assembled. The catalyst coating method was as follows: 162 mg of multi-walled carbon nanotubes were weighed and dispersed in 8 mL of water, 8 mL of ethanol and 1 mL of 5 wt% Nafion solution. After sonication for 30 min, a uniform slurry was prepared. The prepared slurry was coated on the carbon-based material surface of the gas diffusion electrode in three coats. After each coat, the slurry was allowed to dry naturally. The slurry was used up after the three coats.

[0044] Finally, conductive copper tape is bonded to the top of one side of the catalyst layer to form an "L"-shaped metal sheet frame.

[0045] The resulting gas diffusion electrode structure is as follows Figure 1 As shown.

[0046] Example 2 Except for changing the hydrophobic and breathable composite membrane material to polytetrafluoroethylene / polyvinylidene fluoride, the rest of the process is the same as in Example 1.

[0047] Example 3 Except for replacing the hydrophobic and breathable composite membrane material with polytetrafluoroethylene / polydimethylsiloxane, the rest of the process is the same as in Example 1.

[0048] Example 4 Except for changing the hot pressing time to 5 minutes, the rest of the process is the same as in Example 1.

[0049] Example 5 Except for changing the hot pressing temperature to 150 ℃, the rest of the process is the same as in Example 1.

[0050] Comparative Example 1 Except for the fact that only "U"-shaped sealing membrane frames are added to both sides of the carbon-based material (without preparing a gas diffusion layer), the rest of the process is the same as in Example 1.

[0051] Comparative Example 2 Except for not adding the "U"-shaped sealing film frame, the rest of the process is the same as in Example 1.

[0052] Comparative Example 3 Except for not bonding the “L”-shaped metal sheet frame, the rest of the process is the same as in Example 1.

[0053] Comparative Example 4 Except for the hydrophobic and breathable membrane material being changed to polytetrafluoroethylene, the rest of the process is the same as in Example 1.

[0054] Comparative Example 5 Except for changing the hot pressing time to 1 min, the rest of the process is the same as in Example 1.

[0055] The electrodes from Examples 1-5 and Comparative Examples 1-5 were placed in different reactors containing both gas and liquid chambers, with ruthenium-iridium titanium plates used for the corresponding anodes. Air was introduced into the gas chamber, and 0.05 M sodium sulfate electrolyte was introduced into the liquid chamber. A regulated power supply was used with a cell voltage of 3 V. The concentration of hydrogen peroxide in the effluent was measured, and the synthesis rate and current efficiency were calculated. The results are as follows: Figure 2 As shown in the figure. Among them, the hydrophobic and breathable membrane of Comparative Example 4 could not be tightly bonded to the carbon cloth, so the electrochemical performance could not be tested; the results also illustrate the necessity of using a hydrophobic and breathable composite membrane (composite material).

[0056] Compared with Comparative Example 1, Example 1 showed a normalized hydrogen peroxide synthesis rate of 962 mmol·g with a gas diffusion layer. cat -1 ·h -1 The normalized hydrogen peroxide synthesis rate without a gas diffusion layer is only 185 mmol·g. cat -1 ·h -1 The synthesis rate increased by nearly five times. Furthermore, the current efficiency also increased from 31% to 89%. This is because without a gas diffusion layer, the electrode experiences a significant "flooding effect," making it difficult for oxygen to diffuse to the catalyst layer, thus greatly increasing the proportion of current consumed by competing reactions (such as the hydrogen evolution reaction). Additionally, after disassembling the reaction apparatus 5 hours after electrosynthesis, no electrolyte entered the gas chamber when a gas diffusion layer was present, while electrolyte entered the gas chamber when no gas diffusion layer was present.

[0057] Compared to Comparative Example 2, Example 1 showed only slight differences in the normalized hydrogen peroxide synthesis rate and current efficiency with and without the "U"-shaped sealing membrane frame. However, in Comparative Example 2, electrolyte slowly leaked from the edge of the gas diffusion electrode, while this phenomenon did not occur at all in Example 1.

[0058] Compared to Comparative Example 3, Example 1 showed only a slight difference in current efficiency with and without the "L"-shaped metal sheet frame, but the normalized hydrogen peroxide synthesis rate was 962 mmol·g⁻¹. cat-1 ·h -1 and 546 mmol·g cat -1 ·h -1 This is because adding an "L"-shaped metal sheet frame makes the current density distribution on the conductive carbon-based material more uniform, the charge transfer efficiency higher, and the macroscopic manifestation is a larger current, increasing the synthesis rate by nearly 100%.

[0059] Furthermore, compared to Examples 1 and 4 and Comparative Example 5, Comparative Example 5 had a hot-pressing time of only 1 min, which was insufficient, resulting in a synthesis rate of 679 mmol·g⁻¹. cat -1 ·h -1 The synthesis rate in Example 5 was significantly lower than that in Examples 1 and 4, while the synthesis rate and current efficiency in Examples 1 and 4 were similar, indicating that hot pressing for 3 minutes was sufficient in this specific case. Comparing Examples 1 and 5, the synthesis rate in Example 5 (476 mmol·g) was significantly lower than that in Examples 1 and 4, while the synthesis rate and current efficiency in Examples 1 and 4 were similar, indicating that hot pressing for 3 minutes was sufficient in this specific situation. cat -1 ·h -1 Both the current efficiency (53%) and the current efficiency (53%) were lower than those of Example 1. This may be because the rate at which the polymer of the composite film melts and penetrates into the carbon fiber network at the hot pressing temperature of 150 °C is not as fast as that of Example 1. A certain degree of "flooding" occurred during electrosynthesis, resulting in insufficient oxygen transport.

[0060] In summary, this invention relates to a method for preparing a gas diffusion electrode and its application. The gas diffusion electrode comprises a hydrophobic and gas-permeable composite membrane, a carbon substrate layer, a catalyst layer, an "L"-shaped metal sheet frame, and a "U"-shaped sealing membrane frame. When preparing the hydrophobic and gas-permeable composite membrane and the "U"-shaped sealing membrane frame on the carbon substrate, a hot-pressing method is used to ensure full adhesion between the carbon substrate layer and the other two components. When preparing the catalyst layer, the catalyst is prepared into a uniform slurry and coated onto the surface of the carbon substrate layer. The "L"-shaped metal sheet frame is then bonded to the top of the carbon substrate layer. The gas diffusion electrode prepared by this invention can effectively promote gas diffusion to the catalyst layer to participate in the reaction and prevent electrode failure due to water flooding. When applied to the oxygen reduction electrosynthesis of hydrogen peroxide, this invention can increase the yield of electrosynthesized hydrogen peroxide by 5 times.

[0061] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A gas diffusion electrode, characterized in that, It includes a carbon substrate layer (1), a catalyst layer (2), a hydrophobic and breathable membrane (3), a sealing membrane frame (4), and an electrical connection frame (5). The catalyst layer (2) and the hydrophobic and breathable membrane (3) are respectively disposed on both sides of the carbon substrate layer (1); The sealing film frame (4) and the electrical connection frame (5) are disposed on the same side surface of the carbon substrate layer (1) as the catalyst layer (2). The sealing film frame (4) and the electrical connection frame (5) form a closed frame and surround the catalyst layer (2). The catalyst layer (2) does not directly contact the electrical connection frame (5). The outer edge of the hydrophobic and breathable membrane (3) and the closed frame is not less than the outer edge of the carbon substrate layer (1); The hydrophobic and breathable membrane (3), the carbon substrate layer (1), and the sealing membrane frame (4) are compositely formed by hot pressing, so that the three are tightly bonded together.

2. The gas diffusion electrode according to claim 1, characterized in that, The carbon substrate (1) is carbon fiber cloth, carbon felt or carbon paper, and the thickness of the carbon substrate (1) is 0.1-1 mm.

3. The gas diffusion electrode according to claim 1, characterized in that, The hydrophobic and breathable membrane (3) is a composite material, which is composed of polytetrafluoroethylene or expanded polytetrafluoroethylene with a melting temperature higher than the hot pressing temperature and polyvinylidene fluoride, polyethylene, polypropylene or polydimethylsiloxane with a melting temperature lower than the hot pressing temperature; the thickness of the hydrophobic and breathable membrane (3) is 50-500 μm and the pore size is 0.05-5 μm.

4. A gas diffusion electrode according to claim 1, characterized in that, The sealing membrane frame (4) and the hydrophobic and breathable membrane (3) are made of the same material; The sealing membrane frame (4) has a U-shaped structure and is arranged around the catalyst layer (2).

5. A gas diffusion electrode according to claim 1, characterized in that, The carbon substrate layer (1) is made of a metal with good electrical conductivity, including copper and aluminum; The carbon substrate (1) has an L-shaped structure, and one end of the carbon substrate (1) is connected to an external power source.

6. A gas diffusion electrode according to claim 1, characterized in that, The catalyst layer (2) is made of a catalyst material with two-electron oxygen reduction performance, including carbon-based metal single atoms or metal clusters, metal-organic framework materials, covalent organic framework materials and metal oxides; The catalyst loading of the catalyst layer (2) is 0.1-5 mg / cm³. 2 .

7. A method for preparing a gas diffusion electrode as described in any one of claims 1-6, characterized in that, Includes the following steps: S1: The hydrophobic breathable membrane (3), carbon substrate layer (1) and sealing membrane frame (4) are composite molded by hot pressing, so that the hydrophobic polymer of the hydrophobic breathable membrane (3) melts and penetrates into the carbon fiber pores of the carbon substrate layer (1) to form a mechanical interlocking structure. S2: Prepare catalyst slurry and coat it on one side of the carbon substrate layer (1) with the sealing membrane frame (4), and let it dry naturally to form catalyst layer (2). S3: Attach the electrical connection frame (5) to one side of the carbon substrate layer (1) which is composite with the sealing film frame (4), so that the sealing film frame (4) and the electrical connection frame (5) surround the catalyst layer (2).

8. The method for preparing a gas diffusion electrode according to claim 7, characterized in that, The catalyst slurry is prepared through the following steps: S21: The catalyst is dispersed in ethanol / water or isopropanol / water and ultrasonically prepared to form a catalyst slurry; S22: Add Nafion solution to the catalyst slurry to prepare the catalyst slurry; The water-to-ethanol ratio of ethanol / water or isopropanol / water is 10%-90%, the catalyst content in the catalyst slurry is 2-20 mg / mL, and the ultrasonication time is 10-30 min.

9. The method for preparing a gas diffusion electrode according to claim 7, characterized in that, The conditions for the hot pressing method are: pressure 1-10 MPa, hot pressing temperature 150-250 ℃, and hot pressing time 3-10 min.

10. The application of a gas diffusion electrode as described in any one of claims 1-6 in a gas-involved electrochemical reaction.

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